Nitride semiconductor laser element

ABSTRACT

A nitride semiconductor laser element capable of controlling the lateral confinement of light with a good reproducibility, the nitride semiconductor element comprising an n-type cladding layer ( 3 ), an MQW light emitting layer ( 4 ) formed on the cladding layer ( 3 ), a p-type cladding layer ( 5 ) and a p-type contact layer ( 6 ) formed on the light emitting layer ( 4 ), and an ion implantation light absorbing layer ( 7 ) formed, by introducing carbon, in regions other than a current passing region ( 8 ) in the cladding layer ( 5 ) and the contact layer ( 6 ).

TECHNICAL FIELD

The present invention relates to a nitride semiconductor laser element,and more particularly, it relates to a nitride semiconductor laserelement having a light absorption layer.

BACKGROUND TECHNIQUE

A nitride semiconductor laser element has recently been expected forutilization as the light source for an advanced large capacity opticaldisk, and is increasingly subjected to development.

FIG. 173 is a sectional view showing the structure of a conventionalnitride semiconductor laser element. The structure of the conventionalsemiconductor laser element is described with reference to FIG. 173. Inthis conventional nitride semiconductor laser element, an n-type contactlayer 1002 of n-type GaN, an n-type cladding layer 1003 of n-type AlGaN,an MQW (Multiple Quantum Well: multiple quantum well) active layer 1004of InGaN and a p-type cladding layer 1005 having a projecting portionand consisting of p-type AlGaN are formed on a sapphire substrate 1001.The projecting portion of the p-type cladding layer 1005 and the p-typecontact layer 1006 form a ridge portion 1020 serving as a currentpassing region (current path).

A current blocking layer 1007 consisting of a dielectric such as SiO₂ isformed to have an opening on an exposed upper surface portion of then-type contact layer 1002 and to cover the overall surface excluding theupper surface of the p-type contact layer 1006. A p-side ohmic electrode1008 is formed on the p-type contact layer 1006. A p-side pad electrode1009 is formed to be in contact with the upper surface of this p-sideohmic electrode 1008. An n-side ohmic electrode 1010 is formed to be incontact with the upper surface portion of the n-type contact layer 1002exposed in the opening of the current blocking layer 1007. An n-side padelectrode 1011 is formed on this n-side ohmic electrode 1010.

The conventional nitride semiconductor laser element limits the currentpassing region and transversely confines light with the ridge portion1020 and the current blocking layer 1007. In other words, the p-typecladding layer 1005 having the projecting portion is different inthickness between the portion of the p-type cladding layer 1005constituting the ridge portion 1020 forming the current passing regionand the remaining portions. Thus, transverse refractive index differencecan be so provided that transverse optical confinement can be performed.Further, the current passing region can be limited with the currentblocking layer 1007. The width of the current passing region and thetransverse refractive index difference, strongly influencing thecharacteristics of the laser element, must be strictly controlled. Inthe conventional structure shown in FIG. 173, the width of the currentpassing region is controlled through the ridge portion 1020. Further,the transverse refractive index difference is controlled through thewidth of the ridge portion 1020 and the thickness of the p-type claddinglayer 1005 on the portions other than the ridge portion 1020. In thiscase, the thickness of the p-type cladding layer 1005 on the portionsother than the ridge portion 1020 is controlled through the etchingdepth of the p-type cladding layer 1005 in formation of the ridgeportion 1020. In the conventional nitride semiconductor laser element,it has been necessary to precisely control the etching depth of thep-type cladding layer 1005 on the order of 0.01 μm, in order to obtainexcellent element characteristics.

A method of forming a high resistance region in an element by ionimplantation is also known as a technique of controlling the width of acurrent passing region. Such methods are disclosed in Japanese PatentLaying Open No. 9-45962 and Japanese Patent Laying-Open No. 11-214800.

In the conventional structure shown in FIG. 173, however, there has beensuch a disadvantage that it is so difficult to strictly control theetching depth that it is difficult to control transverse opticalconfinement with excellent reproducibility. Consequently, thefabrication yield of the nitride semiconductor laser element hasdisadvantageously been reduced.

In the technique of controlling the width of a current passing regiondisclosed in the aforementioned Japanese Patent Laying Open No. 9-45962or Japanese Patent Laying-Open No. 11-214800, transverse opticalconfinement is not particularly taken into consideration. A laserstructure performing only current narrowing controlling the width ofsuch a current passing region is generally referred to as a gainwaveguide structure. In this gain waveguide structure, there has beensuch a problem that transverse optical confinement is unstabilized.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a nitride semiconductorlaser element capable of controlling transverse optical confinement withexcellent reproducibility.

Another object of the present invention is to improve the yield of theelement in the aforementioned nitride semiconductor laser element.

In order to attain the aforementioned objects, a nitride semiconductorlaser element according to an aspect of the present invention comprisesa first nitride semiconductor layer, an emission layer formed on thefirst nitride semiconductor layer, a second nitride semiconductor layerformed on the emission layer and a light absorption layer formed byintroducing a first impurity element into at least parts of regions ofthe first nitride semiconductor layer and the second nitridesemiconductor layer other than a current passing region.

In the nitride semiconductor laser element according to this aspect, ashereinabove described, the light absorption layer is formed byintroducing the first impurity element into at least the parts of theregions of the first nitride semiconductor layer and the second nitridesemiconductor layer other than the current passing region so that thelight absorption layer can be formed with excellent reproducibility whenthe light absorption layer is formed by introducing the first impurityelement by ion implantation, for example, since ion implantation isexcellent in reproducibility. Thus, transverse optical confinement canbe controlled with excellent reproducibility. Consequently, the yieldcan be improved as compared with a conventional nitride semiconductorlaser element having a ridge portion. Further, no unevenness orhigh-concentration crystal defects are present on the interface betweenthe light absorption layer formed by introducing the first impurityelement and the current passing region dissimilarly to the conventionalstructure having the ridge portion, whereby generation of a leakagecurrent can be remarkably suppressed. In addition, the light absorptionlayer is so formed by introducing the first impurity element that noconventional projecting ridge portion is present, whereby no suchdisadvantage is caused that the element characteristics are deteriorateddue to stress applied to a projecting ridge portion and heat radiationcharacteristics are deteriorated due to reduction of a contact area witha heat radiation base resulting from the projecting ridge portion whenthe laser element is mounted on the heat radiation base from the surfaceside of the element closer to the emission layer in a junction-downsystem.

In the aforementioned nitride semiconductor laser element, the uppersurface of the light absorption layer and the upper surface of thecurrent passing region are preferably formed substantially on the sameplane. According to this structure, unevenness on the element surfacecan be easily reduced. Thus, stress applied to a projecting portion canbe reduced as compared with a conventional ridge structure when thelaser element is mounted on the heat radiation base from the surfaceside of the element closer to the emission layer in the junction-downsystem, whereby the element characteristics can be inhibited fromdeterioration resulting from the stress. Further, the contact area withthe heat radiation base can be increased by reducing the unevenness onthe element surface, whereby excellent heat radiation characteristicscan be obtained.

In the aforementioned nitride semiconductor laser element, the secondnitride semiconductor layer preferably has a projecting ridge portionincluding the current passing region. According to this structure, thelight absorption layer can be formed on the region of the second nitridesemiconductor layer other than the ridge portion with excellentreproducibility when forming the light absorption layer by introducingthe first impurity element into the region of the second nitridesemiconductor layer other than the ridge portion by ion implantation,for example, since ion implantation is excellent in reproducibility.Thus, transverse optical confinement can be controlled with excellentreproducibility. Consequently, the transverse mode can be stabilizedwith excellent reproducibility while performing current narrowingthrough the ridge portion. Further, the transverse mode can be sostabilized that outbreak of kinks (bending of current-light outputcharacteristics) resulting from higher mode oscillation can besuppressed. Thus, a high-maximum light output can be obtained while abeam shape can be stabilized.

In the aforementioned nitride semiconductor laser element, the side endsof the light absorption layer are preferably substantially locatedimmediately under the side ends of the ridge portion. According to thisstructure, the width of current narrowing and the width of opticalconfinement can be substantially equalized with each other, whereby thelaser element can excellently perform current narrowing and lightabsorption through the light absorption layer.

In the aforementioned nitride semiconductor laser element, the side endsof the light absorption layer are preferably provided on positionsseparated at prescribed intervals from the side ends of the ridgeportion. According to this structure, the interval between lightabsorption layers (width of optical confinement) can be rendered largerthan the width of the ridge portion (width of current narrowing),whereby a portion, located immediately under the ridge portion, havinghigh light intensity can be inhibited from excess light absorption whilecurrent narrowing can be strengthened. Thus, increase of a thresholdcurrent can be further suppressed.

In the aforementioned nitride semiconductor laser element, the lightabsorption layer is preferably provided on each side surface of theridge portion. According to this structure, not only current narrowingbut also transverse optical confinement can be performed through theridge portion due to the light absorption layers provided on both sidesurfaces of the ridge portion.

In the aforementioned nitride semiconductor laser element, the ridgeportion may be preferably formed before introducing the first impurityelement. According to this structure, the implantation depth may not beincreased when forming the light absorption layer by introducing thefirst impurity element into the region of the second nitridesemiconductor layer other than the ridge portion by ion implantation,for example, whereby implantation energy can be reduced. Thus, thespreading width of an impurity profile can be so reduced that theimplantation depth can be precisely controlled. Consequently, theimpurity element can be prevented from reaching the emission layer,whereby the emission layer can be prevented from damage by the impurityelement.

In the aforementioned nitride semiconductor laser element, the ridgeportion may be preferably formed after introducing the first impurityelement. According to this structure, it is necessary to form a lightabsorption layer having an implantation depth exceeding the height ofthe ridge portion by increasing implantation energy when forming thelight absorption layer by introducing the first impurity element intothe region of the second nitride semiconductor layer other than a ridgeportion forming region by ion implantation, for example. In this case,the implantation energy is so increased that the spreading width of theimpurity profile is increased. Thus, a profile in the vicinity of a peakdepth of impurity concentration can be so flattened that the lightabsorption function of the light absorption layer can be flattened(uniformized). Consequently, transverse optical confinement can bestabilized.

In the aforementioned nitride semiconductor laser element, the lightabsorption layer preferably has a larger number of crystal defects thanthe current passing region. According to this structure, the laserelement light absorption can be performed through the crystal defectslargely contained in the light absorption layer.

In the aforementioned nitride semiconductor laser element, the lightabsorption layer preferably has a current blocking function. Accordingto this structure, transverse optical confinement and current narrowingcan be simultaneously performed.

The aforementioned nitride semiconductor laser element preferablyfurther comprises a current blocking layer formed by introducing asecond impurity element into at least parts of the regions of the firstnitride semiconductor layer and the second nitride semiconductor layerother than the current passing region. When forming the current blockinglayer independently of the light absorption layer in this manner, thewidth of optical confinement and the width of the current passing regioncan be rendered different from each other.

In the aforementioned nitride semiconductor laser element, the lightabsorption layer is preferably formed by ion-implanting the firstimpurity element into the regions of the first nitride semiconductorlayer and the second nitride semiconductor layer other than the currentpassing region. When forming the light absorption layer by ionimplantation in this manner, the light absorption layer can be easilyformed with excellent reproducibility.

In the aforementioned nitride semiconductor laser element, the lightabsorption layer has either high resistance or a reverse conductivity tothe current passing region. According to this structure, the lightabsorption layer can be easily provided with a current blockingfunction.

In the nitride semiconductor laser element according to theaforementioned aspect, the first impurity element may be an impurityelement other than group 3 and group 5 elements.

In the nitride semiconductor laser element according to theaforementioned aspect, the first impurity element may be an impurityelement having a larger mass number than carbon. According to thisstructure, channeling of ions can be so prevented that impurity ions canbe inhibited from deep implantation. Consequently, controllability foran implantation profile in the depth direction can be improved.

In the nitride semiconductor laser element according to theaforementioned aspect, the maximum value of the impurity concentrationof the first impurity element may be at least 5.0×10¹⁹ cm⁻³. Accordingto this structure, crystal defects can be generated in the lightabsorption layer with sufficient density, whereby the absorptioncoefficient of the light absorption layer can be sufficiently increased.Thus, transverse optical confinement can be sufficiently performed.

In the nitride semiconductor laser element according to theaforementioned aspect, the maximum value of crystal defect density of atleast either the first nitride semiconductor layer or the second nitridesemiconductor layer containing the first impurity element may be atleast 5×10¹⁸ cm⁻³. According to this structure, the light absorptioncoefficient is so sufficiently increased that transverse opticalconfinement can be sufficiently performed.

In the nitride semiconductor laser element according to theaforementioned aspect, the maximum value of the absorption coefficientof the light absorption layer may be at least 1×10⁴ cm⁻¹. According tothis structure, transverse optical confinement can be sufficientlyperformed.

The nitride semiconductor laser element according to the aforementionedaspect is heat-treated after introduction of the first impurity element.According to this structure, the absorption coefficient can be easilycontrolled. In this case, the absorption coefficient may be reduced bythe heat treatment.

In the nitride semiconductor laser element according to theaforementioned aspect, the light absorption layer is formed by ionimplantation from a direction inclined from the [0001] direction of anitride semiconductor. According to this structure, channeling of ionscan be so prevented that impurity ions can be inhibited from deepimplantation. Consequently, controllability for an implantation profilein the depth direction can be improved. In this case, the surface of thenitride semiconductor is the (0001) plane, the light absorption layer isformed excluding a striped width, and ion implantation is performed froma direction inclined from the [0001] direction of the nitridesemiconductor in a plane including a stripe direction not formed withlight absorption layer and a direction perpendicular to the surface ofthe nitride semiconductor. Thus, channeling of ions can be preventedwhile preventing the ions from asymmetrical implantation into a lowerportion of a mask for forming the light absorption layer excluding thestriped width.

In the nitride semiconductor laser element according to theaforementioned aspect, the current blocking layer may consist of anitride semiconductor having high resistance. According to thisstructure, a high-resistance layer can be easily formed by introducinghydrogen into a region containing a p-type dopant, for example, wherebythe current blocking layer can be easily formed.

In the nitride semiconductor laser element according to theaforementioned aspect, the current passing region may have a p type, andthe current blocking layer may contain hydrogen in higher density thanthe current passing region. According to this structure, the currentblocking layer can be easily formed by introducing hydrogen into theregion containing the p-type dopant. In this case, the current blockinglayer containing hydrogen in higher density than the current passingregion may be formed by performing heat treatment in an atmospherecontaining hydrogen. According to this structure, the current blockinglayer can be easily formed by diffusion of hydrogen. In this case,crystal defects are more hardly introduced through diffusion thanthrough ion implantation, whereby reliability of the element can beimproved. In particular, the light absorption layer may be formedexcluding a first width, a current narrowing layer may be formedexcluding a second width, a region of the second width may be formed ina region of the first width and the first width may be rendered largerthan the second width. Further, the current narrowing layer may beformed separately from the emission layer by a second distance in thedepth direction, the light absorption layer may be formed separatelyfrom the emission layer by a first distance in the depth direction, andthe first distance may be formed to be larger than the second distance.According to this structure, crystal defects of a region close to theemission layer can be reduced, whereby the aforementioned effect ofimproving the reliability of the element by hydrogen diffusion is large.

In the nitride semiconductor laser element according to theaforementioned aspect, the current blocking layer has a reverseconductivity type to the current passing region. According to thisstructure, a nitride semiconductor of the reverse conductivity type canbe easily formed by introducing a dopant of the reverse conductivitytype to the current passing region into the current blocking layer, forexample, whereby the current blocking layer can be easily formed.

In the nitride semiconductor laser element according to theaforementioned aspect, the second impurity element may be an impurityelement other than group 3 and 5 elements. In this case, the secondimpurity element may be an element different from the first impurityelement. According to this structure, the introduced impurity elementsare so different from each other that concentration profiles of thefirst impurity element and the second impurity element can be easilyrendered different from each other. Therefore, the shape of the lightabsorption layer and the shape of the current blocking layer can beeasily controlled. Further, the conductivity type of the currentblocking layer can be easily controlled. In formation of the currentblocking layer, further, crystal defects can be prevented from excessformation by ion-implanting a relatively light element. In formation ofthe light absorption layer, on the other hand, crystal defects can beintroduced with a low dose by ion-implanting a relatively heavy element,whereby the introduced element can be prevented from diffusing into theemission layer and exerting bad influence on the characteristics of theelement dissimilarly to a case of a high dose (high concentration).

In the nitride semiconductor laser element according to theaforementioned aspect, the current blocking layer is formed byion-implanting the second impurity element. According to this structure,the impurity element can be introduced from the surface up to a deepposition by ion implantation. While a limited element such as a dopantelement must be employed in diffusion, ion implantation advantageouslyprovides a wide range of selection for implanted elements.

In the nitride semiconductor laser element according to theaforementioned aspect, the current blocking layer is formed byion-implanting the second impurity element into the lower portion of amask layer obliquely from above. According to this structure, the lightabsorption layer is formed excluding the first width while the currentnarrowing layer is formed excluding the second width, the first width islarger than the second width, and a region of the second width is formedin a region of the first width. Thus, the width of a current passingregion can be reduced beyond the width of optical confinement.Consequently, light absorption by the light absorption layer can bereduced while simultaneously strengthening current narrowing, wherebyreduction of the threshold current and improvement of slope efficiencycan be attained.

In the nitride semiconductor laser element according to theaforementioned aspect, the current blocking layer is formed by diffusingthe second impurity element. In this case, crystal defects are morehardly introduced through diffusion than through ion implantation,whereby reliability of the element can be improved. In particular, thecurrent narrowing layer may be formed excluding a second width, thelight absorption layer may be formed excluding a first width, a regionof the second width may be formed in a region of the first width and thefirst width may be rendered larger than the second width. Further, thecurrent narrowing layer may be formed separately from the emission layerby a second distance in the depth direction, the light absorption layermay be formed separately from the emission layer by a first distance inthe depth direction, and the first distance may be formed to be largerthan the second distance. According to this structure, crystal defectsof a region close to the emission layer can be reduced, whereby theaforementioned effect of improving the reliability of the element bydiffusion is large.

In the nitride semiconductor laser element according to theaforementioned aspect, the light absorption layer may be formedexcluding a first width while the current narrowing layer may be formedexcluding a second width, the first width may be larger than the secondwidth, and a region of the second width may be formed in a region of thefirst width. Thus, light absorption by the light absorption layer can bereduced while simultaneously strengthening current narrowing, wherebyreduction of the threshold current and improvement of the slopeefficiency can be attained.

In the nitride semiconductor laser element according to theaforementioned aspect, the light absorption layer may be formedseparately from the emission layer by a first distance in the depthdirection while the current blocking layer may be formed separately fromthe emission layer by a second distance in the depth direction, and thefirst distance may be rendered larger than the second distance.According to this structure, the width of the current passing region canbe inhibited from exceeding the width of optical confinement. Thus,light absorption by the light absorption layer can be reduced whilesimultaneously strengthening current narrowing, whereby reduction of thethreshold current and improvement of the slope efficiency can beattained. In this case, the second distance may be zero, and the currentblocking layer may be formed in the emission layer.

In the nitride semiconductor laser element according to theaforementioned aspect, the concentration of the second impurity elementin the current blocking layer may be lower than the concentration of thefirst impurity element in the light absorption layer. According to thisstructure, the density of crystal defects in the current blocking layercan be reduced beyond the density of crystal defects in the lightabsorption layer when implanting the second impurity element into thecurrent blocking layer by ion implantation, whereby light absorption inthe current blocking layer can be sufficiently reduced. Thus,unnecessary light absorption in the current blocking layer can besuppressed.

In the nitride semiconductor laser element according to theaforementioned aspect, the density of crystal defects in the currentblocking layer may be lower than the density of crystal defects in thelight absorption layer. According to this structure, light absorption inthe current blocking layer can be so sufficiently reduced thatunnecessary light absorption in the current blocking layer can besuppressed.

In the nitride semiconductor laser element according to theaforementioned aspect, the impurity concentration of the first impurityelement in a portion of the emission layer corresponding to an upper orlower region of the light absorption layer may be not more than 5.0×10¹⁸cm⁻³. According to this structure, crystal defects in the portion of theemission layer corresponding to the upper or lower region of the lightabsorption layer can be so reduced that the life of the element can beimproved.

In the nitride semiconductor laser element according to theaforementioned aspect, the density of crystal defects in a portion ofthe emission layer located on an upper or lower region of the lightabsorption layer may be not more than 5.0×10¹⁷ cm⁻³. According to thisstructure, the number of crystal defects in the portion of the emissionlayer located on the upper or lower region of the light absorption layeris so small that the life of the element can be improved.

In the nitride semiconductor laser element according to theaforementioned aspect, the first nitride semiconductor layer and thesecond nitride semiconductor layer include a cladding layer, and theconcentration of the first impurity element is maximized in the claddinglayer. According to this structure, crystal defects can be formed in thecladding layer with sufficient concentration, whereby a light absorptionlayer having a sufficient light absorption effect can be formed in thecladding layer. Light exudes into the cladding layer to some extent,whereby the light can be effectively absorbed by providing the lightabsorption layer in the cladding layer. Therefore, the element has asufficient transverse optical confinement effect while the number ofcrystal defects is small in the portion of the emission layercorresponding to the upper or lower region of the light absorptionlayer, whereby the life of the element can be improved.

In the nitride semiconductor laser element according to theaforementioned aspect, the light absorption layer may be so formed thatthe light absorption layer is not formed in the emission layer. Morepreferably, the light absorption layer may be formed separately from theemission layer by a finite first distance larger than zero in the depthdirection. According to this structure, the number of crystal defects isso small in the portion of the emission layer corresponding to the upperor lower region of the light absorption layer that the life of theelement can be improved.

In the nitride semiconductor laser element according to theaforementioned aspect, the first nitride semiconductor layer and thesecond nitride semiconductor layer include a cladding layer, and thedensity of crystal defects in the light absorption layer is maximized inthe cladding layer. According to this structure, a light absorptionhaving a sufficient light absorption effect can be formed in thecladding layer. According to this structure, the number of crystaldefects is so small in the portion of the emission layer correspondingto the upper or lower region of the light absorption layer, that thelife of the element can be improved.

In the nitride semiconductor laser element according to theaforementioned aspect, the first nitride semiconductor layer and thesecond nitride semiconductor layer include a cladding layer, and thelight absorption coefficient of the light absorption layer is maximizedin the cladding layer. According to this structure, the element has asufficient transverse optical confinement effect while the number ofcrystal defects is so small in the portion of the emission layercorresponding to the upper or lower region of the light absorption layerthat the life of the element can be improved.

In the nitride semiconductor laser element according to theaforementioned aspect, the emission layer is formed on the first nitridesemiconductor layer after the first impurity element is introduced intothe first nitride semiconductor layer. According to this structure,transverse optical confinement can be performed on thefirst-nitride-semiconductor-layer side. Further, no ion implantation isperformed on the emission layer so that the number of defects in theemission layer can be reduced, whereby the life of the element can beimproved as a result. In a structure not implanting ions into a contactlayer on the second-nitride-semiconductor-layer side, the contact layeron the second-nitride-semiconductor-layer side having low defectconcentration can be formed with a wide area. Therefore, the carrierconcentration of the contact layer on thesecond-nitride-semiconductor-layer side can be so improved that acontact area between the contact layer on thesecond-nitride-semiconductor-layer side and an electrode can be widened.Consequently, contact resistance on thesecond-nitride-semiconductor-layer-side can be reduced.

In the nitride semiconductor laser element according to theaforementioned aspect, the impurity concentration of the first impurityelement may be maximized in the emission layer. According to thisstructure, strong complex refractive index difference can be formed inthe in-plane direction of the emission layer, whereby the dose of thefirst impurity element can be reduced.

In the nitride semiconductor laser element according to theaforementioned aspect, the density of crystal defects may be maximizedin the emission layer. According to this structure, strong complexrefractive index difference can be formed in the in-plane direction ofthe emission layer, whereby the dose of the first impurity element canbe reduced.

In the nitride semiconductor laser element according to theaforementioned aspect, the light absorption coefficient of the lightabsorption layer may be maximized in the emission layer. According tothis structure, strong complex refractive index difference can be formedin the in-plane direction of the emission layer, whereby the dose of thefirst impurity element may be small.

In the nitride semiconductor laser element according to theaforementioned aspect, a contact layer is formed on the second nitridesemiconductor layer after the light absorption layer is formed byintroducing the first impurity element into the second nitridesemiconductor layer on the emission layer. According to this structure,no ion implantation is performed on the contact layer located upwardbeyond the emission layer, whereby the contact layer having a smallnumber of crystal defects can be formed with a wide area. Thus, thecarrier concentration of the contact layer located upward beyond theemission layer can be so improved that contact resistance between thecontact layer located upward beyond the emission layer and an electrodelayer can be reduced.

In the nitride semiconductor laser element according to theaforementioned aspect, the first impurity element is ion-implantedthrough a through film. According to this structure, channeling of ionscan be so prevented that impurity ions can be inhibited from deepimplantation.

In the nitride semiconductor laser element according to theaforementioned aspect, the through film may be an insulator film.According to this structure, the insulator film employed for the throughfilm can be utilized as an insulator film on the light absorption layeror the current blocking layer, whereby current blocking can be morereliably performed.

In the nitride semiconductor laser element according to theaforementioned aspect, the first impurity element is ion-implantedthrough a through film having a first ion permeation region having firststopping power and a second ion permeation region having second stoppingpower more hardly permeating ions than the first ion permeation region.According to this structure, regions having different implantationdepths can be simultaneously formed through single ion implantation.Thus, a structure having a width of optical confinement and a width ofthe current passing region different from each other can be formedthrough single ion implantation. Therefore, an optical confinementregion and a current blocking region may not be formed through differentsteps respectively, whereby steps can be simplified.

The nitride semiconductor laser element according to the aforementionedaspect employs a first film including a first region having firststopping power and a second region having third stopping power hardlypermeating ions as a through film while employing the said second regionas a mask for ion-implanting the said first impurity element. Accordingto this structure, a non-implanted region of a prescribed width can beeasily formed.

The nitride semiconductor laser element according to the aforementionedaspect further comprises an electrode layer formed on the second nitridesemiconductor layer, while the first impurity element is ion-implantedinto the second nitride semiconductor layer through a through film withthe electrode layer serving as a mask. According to this structure, theelectrode layer serving as a mask layer can be utilized as a contactelectrode, whereby a fabrication process can be simplified.

In the nitride semiconductor laser element according to theaforementioned aspect, an insulator film may be formed on the lightabsorption layer. According to this structure, generation of a smallleakage current can be prevented when a high current is fed to theelement.

In the nitride semiconductor laser element according to theaforementioned aspect, the light absorption layer is formed excluding afirst width, and the nitride semiconductor laser element furthercomprises an electrode layer coming into ohmic contact with the secondnitride semiconductor laser with a width smaller than the first width.According to this structure, the width of a current passing region canbe reduced beyond the width of optical confinement. Thus, lightabsorption by the light absorption layer can be reduced whilesimultaneously strengthening current narrowing, whereby reduction of thethreshold current and improvement of the slope efficiency can beattained.

In the nitride semiconductor laser element according to theaforementioned aspect, the light absorption layer is formed excluding afirst width, and the nitride semiconductor laser element furthercomprises an electrode layer coming into ohmic contact with the secondnitride semiconductor laser with a width larger than the first width.According to this structure, it is possible to improve heat radiationcharacteristics of the element by forming a large-area electrode on thesecond nitride semiconductor layer since an electrode has a high thermalconductivity. Consequently, the life of the element can be improved.Further, the surface of the element can be so flattened that a contactarea with a submount is increased and adhesion is improved when theelement is assembled in the junction-down system, whereby the heatradiation characteristics are improved. It is possible to improve thelife of the element also by this. Further, the contact area of theelectrode layer can be so increased that contact resistance can bereduced.

The nitride semiconductor laser element according to the aforementionedaspect further comprises an electric isolation region of high resistanceformed by introducing a third impurity element into at least part of aregion other than the current passing region over a region passingthrough the emission layer from the surface of the second nitridesemiconductor layer. According to this structure, p-type semiconductorsor a p-type semiconductor and an n-type semiconductor can beelectrically isolated from each other. Therefore, an element having aflat surface on the second-nitride-semiconductor-layer side can beformed. Further, a plurality of elements can be easily integrated.

In the nitride semiconductor laser element according to theaforementioned aspect, the electric isolation region may be formed byion-implanting the third impurity element. According to this structure,the impurity element can be introduced from the surface up to a deepposition in the ion implantation, whereby a deep electric isolationregion can be easily formed.

The nitride semiconductor laser element according to the aforementionedaspect introduces a fourth impurity element into a region other than thecurrent passing region and at least part of a region other than theelectric isolation region over a region passing through the emissionlayer from the surface of the second nitride semiconductor layer so thatthe region passing through the emission layer from the second nitridesemiconductor layer has the same conductivity type as the first nitridesemiconductor layer. According to this structure, the element having aflat surface on the second-nitride-semiconductor-layer side can beeasily formed by forming an electrode on thefirst-nitride-semiconductor-layer side and an electrode on thesecond-nitride-semiconductor-layer side oppositely to the substrate.

In the nitride semiconductor laser element according to theaforementioned aspect, the nitride semiconductor laser element includesa nitride semiconductor laser element, assembled in a junction-downsystem, mounted on a base for heat radiation from the surface of a sidecloser to the emission layer. According to this structure, irregularityon the surface of an element region is so small that stress applied tothe element region can be reduced by assembling the element in thejunction-down system, whereby deterioration of the elementcharacteristics can be suppressed as a result. Further, the element canbe homogeneously welded to a submount or the like when assembled in thejunction-down system, whereby the heat radiation characteristics of theelement are improved.

In the nitride semiconductor laser element according to theaforementioned aspect, the light absorption layer is divided into aplurality of parts between the current passing region and side ends ofthe element. According to this structure, a region for forming the lightabsorption layer can be inhibited from increase, whereby lightabsorption can be inhibited from excessiveness in the vicinity of theemission layer. Consequently, increase of the threshold current can besuppressed.

In the nitride semiconductor laser element according to theaforementioned aspect, a portion of the light absorption layer closer tothe current passing region has a smaller depth than a portion of thelight absorption layer closer to the side ends of the element. Accordingto this structure, light absorption can be further inhibited fromexcessiveness in the vicinity of the emission layer.

In the nitride semiconductor laser element according to theaforementioned aspect, the portion of the light absorption layer closerto the current passing region has a depth not reaching the emissionlayer. According to this structure, light absorption can be easilyinhibited from excessiveness in the vicinity of the emission layer.

In the nitride semiconductor laser element according to theaforementioned aspect, a first width between side ends of the lightabsorption layer in the vicinity of a cavity end surface of the elementis smaller than a second width between side ends of a portion of thelight absorption layer in the vicinity of the central portion of theelement. According to this structure, transverse optical confinement canbe excellently performed on the cavity end surface of the element,whereby a transverse mode can be stabilized. Thus, outbreak of kinks(bending of current-light output characteristics) resulting from highermode oscillation can be suppressed. Further, light absorption in thevicinity of the emission layer can be inhibited from excessiveness atthe central portion of the element, whereby increase of the thresholdcurrent can be suppressed. Consequently, the beam shape can bestabilized while suppressing increase of the threshold current,reduction of slope efficiency and reduction of a kink level.

In the nitride semiconductor laser element according to theaforementioned aspect, a boundary region between a region of the lightabsorption layer having the first width and a region having the secondwidth has a width gradually enlarging to approach from the first widthto the second width. According to this structure, abrupt change of lightabsorption can be so suppressed that coupling loss can be suppressedbetween a portion close to the cavity end surface of the element and aportion close to the central portion of the element. Thus, outputcharacteristics can be inhibited from reduction.

In the nitride semiconductor laser element according to theaforementioned aspect, the boundary region between the region of thelight absorption layer having the first width and the region having thesecond width is formed in a tapered shape in plan view. According tothis structure, the width of the boundary region between the regionhaving the first width and the region having the second width in thelight absorption layer can be formed to be gradually increased toapproach from the first width to the second width.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing the structure of a nitridesemiconductor laser element according to a first embodiment of thepresent invention.

FIG. 2 is an enlarged sectional view showing an MQW emission layer ofthe nitride semiconductor laser element according to the firstembodiment shown in FIG. 1.

FIG. 3 is an enlarged sectional view schematically showing ion-implantedregions.

FIG. 4 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the firstembodiment shown in FIG. 1.

FIG. 5 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the firstembodiment shown in FIG. 1.

FIG. 6 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the firstembodiment shown in FIG. 1.

FIG. 7 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the firstembodiment shown in FIG. 1.

FIG. 8 is a graph showing simulation results of carbon concentration andcrystal defect concentration profiles in the nitride semiconductor laserelement according to the first embodiment shown in FIG. 1.

FIG. 9 is a graph showing results of measurement of the carbonconcentration profile by SIMS in the nitride semiconductor laser elementaccording to the first embodiment shown in FIG. 1.

FIG. 10 is a sectional view showing the structure of a nitridesemiconductor laser element according to a second embodiment of thepresent invention.

FIG. 11 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the secondembodiment shown in FIG. 10.

FIG. 12 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the secondembodiment shown in FIG. 10.

FIG. 13 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the secondembodiment shown in FIG. 10.

FIG. 14 is a sectional view showing the structure of a nitridesemiconductor laser element according to a third embodiment of thepresent invention.

FIG. 15 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the thirdembodiment shown in FIG. 14.

FIG. 16 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the thirdembodiment shown in FIG. 14.

FIG. 17 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the thirdembodiment shown in FIG. 14.

FIG. 18 is a sectional view showing the structure of a nitridesemiconductor laser element according to a fourth embodiment of thepresent invention.

FIG. 19 is a sectional view showing the structure of a nitridesemiconductor laser element according to a fifth embodiment of thepresent invention.

FIG. 20 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the fifthembodiment shown in FIG. 19.

FIG. 21 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the fifthembodiment shown in FIG. 19.

FIG. 22 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the fifthembodiment shown in FIG. 19.

FIG. 23 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the fifthembodiment shown in FIG. 19.

FIG. 24 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the fifthembodiment shown in FIG. 19.

FIG. 25 is a sectional view showing the structure of a nitridesemiconductor laser element according to a sixth embodiment of thepresent invention.

FIG. 26 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the sixthembodiment shown in FIG. 25.

FIG. 27 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the sixthembodiment shown in FIG. 25.

FIG. 28 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the sixthembodiment shown in FIG. 25.

FIG. 29 is a sectional view showing the structure of a nitridesemiconductor laser element according to a seventh embodiment of thepresent invention.

FIG. 30 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the seventhembodiment shown in FIG. 29.

FIG. 31 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the seventhembodiment shown in FIG. 29.

FIG. 32 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the seventhembodiment shown in FIG. 29.

FIG. 33 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the seventhembodiment shown in FIG. 29.

FIG. 34 is a sectional view showing the structure of a nitridesemiconductor laser element according to an eighth embodiment of thepresent invention.

FIG. 35 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the eighthembodiment shown in FIG. 34.

FIG. 36 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the eighthembodiment shown in FIG. 34.

FIG. 37 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the eighthembodiment shown in FIG. 34.

FIG. 38 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the eighthembodiment shown in FIG. 34.

FIG. 39 is a sectional view showing the structure of a nitridesemiconductor laser element according to a ninth embodiment of thepresent invention.

FIG. 40 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the ninthembodiment shown in FIG. 39.

FIG. 41 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the ninthembodiment shown in FIG. 39.

FIG. 42 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the ninthembodiment shown in FIG. 39.

FIG. 43 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the ninthembodiment shown in FIG. 39.

FIG. 44 is a sectional view showing the structure of a nitridesemiconductor laser element according to a tenth embodiment of thepresent invention.

FIG. 45 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the tenthembodiment shown in FIG. 44.

FIG. 46 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the tenthembodiment shown in FIG. 44.

FIG. 47 is a sectional view showing the structure of a nitridesemiconductor laser element according to an eleventh embodiment of thepresent invention.

FIG. 48 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the eleventhembodiment shown in FIG. 47.

FIG. 49 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the eleventhembodiment shown in FIG. 47.

FIG. 50 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the eleventhembodiment shown in FIG. 47.

FIG. 51 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the eleventhembodiment shown in FIG. 47.

FIG. 52 is a sectional view showing the structure of a nitridesemiconductor laser element according to a twelfth embodiment of thepresent invention.

FIG. 53 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the twelfthembodiment shown in FIG. 52.

FIG. 54 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the twelfthembodiment shown in FIG. 52.

FIG. 55 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the twelfthembodiment shown in FIG. 52.

FIG. 56 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the twelfthembodiment shown in FIG. 52.

FIG. 57 is a sectional view showing the structure of a nitridesemiconductor laser element according to a thirteenth embodiment of thepresent invention.

FIG. 58 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the thirteenthembodiment shown in FIG. 57.

FIG. 59 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the thirteenthembodiment shown in FIG. 57.

FIG. 60 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the thirteenthembodiment shown in FIG. 57.

FIG. 61 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the thirteenthembodiment shown in FIG. 57.

FIG. 62 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the thirteenthembodiment shown in FIG. 57.

FIG. 63 is a sectional view showing the structure of a nitridesemiconductor laser element according to a fourteenth embodiment of thepresent invention.

FIG. 64 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the fourteenthembodiment shown in FIG. 63.

FIG. 65 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the fourteenthembodiment shown in FIG. 63.

FIG. 66 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the fourteenthembodiment shown in FIG. 63.

FIG. 67 is a sectional view showing the structure of a nitridesemiconductor laser element according to a fifteenth embodiment of thepresent invention.

FIG. 68 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the fifteenthembodiment shown in FIG. 67.

FIG. 69 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the fifteenthembodiment shown in FIG. 67.

FIG. 70 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the fifteenthembodiment shown in FIG. 67.

FIG. 71 is a sectional view showing the structure of a nitridesemiconductor laser element according to a sixteenth embodiment of thepresent invention.

FIG. 72 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the sixteenthembodiment shown in FIG. 71.

FIG. 73 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the sixteenthembodiment shown in FIG. 71.

FIG. 74 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the sixteenthembodiment shown in FIG. 71.

FIG. 75 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the sixteenthembodiment shown in FIG. 71.

FIG. 76 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the sixteenthembodiment shown in FIG. 71.

FIG. 77 is a sectional view showing the structure of a nitridesemiconductor laser element according to a seventeenth embodiment of thepresent invention.

FIG. 78 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the seventeenthembodiment shown in FIG. 77.

FIG. 79 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the seventeenthembodiment shown in FIG. 77.

FIG. 80 is a sectional view for illustrating the. fabrication processfor the nitride semiconductor laser element according to the seventeenthembodiment shown in FIG. 77.

FIG. 81 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the seventeenthembodiment shown in FIG. 77.

FIG. 82 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the seventeenthembodiment shown in FIG. 77.

FIG. 83 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the seventeenthembodiment shown in FIG. 77.

FIG. 84 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the seventeenthembodiment shown in FIG. 77.

FIG. 85 is a sectional view showing the structure of a nitridesemiconductor laser element according to an eighteenth embodiment of thepresent invention.

FIG. 86 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the eighteenthembodiment shown in FIG. 85.

FIG. 87 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the eighteenthembodiment shown in FIG. 85.

FIG. 88 is a sectional view showing the structure of a nitridesemiconductor laser element according to a nineteenth embodiment of thepresent invention.

FIG. 89 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the nineteenthembodiment shown in FIG. 88.

FIG. 90 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the nineteenthembodiment shown in FIG. 88.

FIG. 91 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the nineteenthembodiment shown in FIG. 88.

FIG. 92 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the nineteenthembodiment shown in FIG. 88.

FIG. 93 is a sectional view showing the structure of a nitridesemiconductor laser element according to a twentieth embodiment of thepresent invention.

FIG. 94 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the twentiethembodiment shown in FIG. 93.

FIG. 95 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the twentiethembodiment shown in FIG. 93.

FIG. 96 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the twentiethembodiment shown in FIG. 93.

FIG. 97 is a sectional view for illustrating the fabrication process forthe nitride semiconductor laser element according to the twentiethembodiment shown in FIG. 93.

FIG. 98 is a sectional view showing the structure of a nitridesemiconductor laser element according to a twenty-first embodiment ofthe present invention.

FIG. 99 is an enlarged sectional view showing an MQW emission layer ofthe nitride semiconductor laser element according to the twenty-firstembodiment shown in FIG. 98.

FIG. 100 is a characteristic diagram showing current-to-optical outputcharacteristics of the nitride semiconductor laser element according tothe twenty-first embodiment shown in FIG. 98 and a conventional(comparative) nitride semiconductor laser element;

FIG. 101 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the twenty-firstembodiment shown in FIG. 98.

FIG. 102 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-first embodiment shown in FIG. 98.

FIG. 103 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-first embodiment shown in FIG. 98.

FIG. 104 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-first embodiment shown in FIG. 98.

FIG. 105 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-first embodiment shown in FIG. 98.

FIG. 106 is a sectional view showing the structure of a nitridesemiconductor laser element according to a twenty-second embodiment ofthe present invention.

FIG. 107 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the twenty-secondembodiment shown in FIG. 106.

FIG. 108 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-second embodiment shown in FIG. 106.

FIG. 109 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-second embodiment shown in FIG. 106.

FIG. 110 is a sectional view showing the structure of a nitridesemiconductor laser element according to a twenty-third embodiment ofthe present invention.

FIG. 111 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the twenty-thirdembodiment shown in FIG. 110.

FIG. 112 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-third embodiment shown in FIG. 110.

FIG. 113 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-third embodiment shown in FIG. 110.

FIG. 114 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-third embodiment shown in FIG. 110.

FIG. 115 is a sectional view showing the structure of a nitridesemiconductor laser element according to a twenty-fourth embodiment ofthe present invention.

FIG. 116 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the twenty-fourthembodiment shown in FIG. 115.

FIG. 117 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-fourth embodiment shown in FIG. 115.

FIG. 118 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-fourth embodiment shown in FIG. 115.

FIG. 119 is a sectional view showing the structure of a nitridesemiconductor laser element according to a twenty-fifth embodiment ofthe present invention.

FIG. 120 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the twenty-fifthembodiment shown in FIG. 119.

FIG. 121 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-fifth embodiment shown in FIG. 119.

FIG. 122 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-fifth embodiment shown in FIG. 119.

FIG. 123 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-fifth embodiment shown in FIG. 119.

FIG. 124 is a sectional view showing the structure of a nitridesemiconductor laser element according to a twenty-sixth embodiment ofthe present invention.

FIG. 125 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the twenty-sixthembodiment shown in FIG. 124.

FIG. 126 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-sixth embodiment shown in FIG. 124.

FIG. 127 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-sixth embodiment shown in FIG. 124.

FIG. 128 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-sixth embodiment shown in FIG. 124.

FIG. 129 is a sectional view showing the structure of a nitridesemiconductor laser element according to a twenty-seventh embodiment ofthe present invention.

FIG. 130 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the twenty-seventhembodiment shown in FIG. 129.

FIG. 131 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-seventh embodiment shown in FIG. 129.

FIG. 132 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-seventh embodiment shown in FIG. 129.

FIG. 133 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-seventh embodiment shown in FIG. 129.

FIG. 134 is a sectional view showing the structure of a nitridesemiconductor laser element according to a twenty-eighth embodiment ofthe present invention.

FIG. 135 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the twenty-eighthembodiment shown in FIG. 134.

FIG. 136 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-eighth embodiment shown in FIG. 134.

FIG. 137 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-eighth embodiment shown in FIG. 134.

FIG. 138 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-eighth embodiment shown in FIG. 134.

FIG. 139 is a sectional view showing the structure of a nitridesemiconductor laser element according to a twenty-ninth embodiment ofthe present invention.

FIG. 140 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the twenty-ninthembodiment shown in FIG. 139.

FIG. 141 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-ninth embodiment shown in FIG. 139.

FIG. 142 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-ninth embodiment shown in FIG. 139.

FIG. 143 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to thetwenty-ninth embodiment shown in FIG. 139.

FIG. 144 is a sectional view showing the structure of a nitridesemiconductor laser element according to a thirtieth embodiment of thepresent invention.

FIG. 145 is a sectional view for illustrating a fabrication process forthe nitride semiconductor laser element according to the thirtiethembodiment shown in FIG. 144.

FIG. 146 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to the thirtiethembodiment shown in FIG. 144.

FIG. 147 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to the thirtiethembodiment shown in FIG. 144.

FIG. 148 is a sectional view for illustrating the fabrication processfor the nitride semiconductor laser element according to the thirtiethembodiment shown in FIG. 144.

FIG. 149 is a sectional view showing the structure of a nitridesemiconductor laser element according to a thirty-first embodiment ofthe present invention.

FIG. 150 is an enlarged sectional view showing an MQW emission layer ofthe nitride semiconductor laser element according to the thirty-firstembodiment shown in FIG. 149.

FIG. 151 is a front elevational view of the nitride semiconductor laserelement according to the thirty-first embodiment shown in FIG. 149.

FIG. 152 is a sectional view of the nitride semiconductor laser elementaccording to the thirty-first embodiment shown in FIG. 149 taken alongthe line 800-800.

FIG. 153 is a plan view showing regions for forming ion-implanted lightabsorption layers of the nitride semiconductor laser element accordingto the thirty-first embodiment shown in FIG. 149.

FIG. 154 is a perspective view for illustrating a fabrication processfor the nitride semiconductor laser element according to thethirty-first embodiment shown in FIG. 149.

FIG. 155 is a perspective view for illustrating the fabrication processfor the nitride semiconductor laser element according to thethirty-first embodiment shown in FIG. 149.

FIG. 156 is a perspective view for illustrating the fabrication processfor the nitride semiconductor laser element according to thethirty-first embodiment shown in FIG. 149.

FIG. 157 is a perspective view for illustrating the fabrication processfor the nitride semiconductor laser element according to thethirty-first embodiment shown in FIG. 149.

FIG. 158 is a perspective view for illustrating the fabrication processfor the nitride semiconductor laser element according to thethirty-first embodiment shown in FIG. 149.

FIG. 159 is a perspective view for illustrating the fabrication processfor the nitride semiconductor laser element according to thethirty-first embodiment shown in FIG. 149.

FIG. 160 is a perspective view for illustrating the fabrication processfor the nitride semiconductor laser element according to thethirty-first embodiment shown in FIG. 149.

FIG. 161 is a perspective view for illustrating the fabrication processfor the nitride semiconductor laser element according to thethirty-first embodiment shown in FIG. 149.

FIG. 162 is a perspective view for illustrating the fabrication processfor the nitride semiconductor laser element according to thethirty-first embodiment shown in FIG. 149.

FIG. 163 is a perspective view for illustrating the fabrication processfor the nitride semiconductor laser element according to thethirty-first embodiment shown in FIG. 149.

FIG. 164 is a perspective view for illustrating the fabrication processfor the nitride semiconductor laser element according to thethirty-first embodiment shown in FIG. 149.

FIG. 165 is a perspective view showing the structure of a nitridesemiconductor laser element according to a thirty-second embodiment ofthe present invention.

FIG. 166 is a front elevational view of the nitride semiconductor laserelement according to the thirty-second embodiment shown in FIG. 165.

FIG. 167 is a sectional view of the nitride semiconductor laser elementaccording to the thirty-second embodiment shown in FIG. 165 taken alongthe line 900-900.

FIG. 168 is a perspective view for illustrating a fabrication processfor the nitride semiconductor laser element according to thethirty-second embodiment shown in FIG. 165.

FIG. 169 is a perspective view for illustrating the fabrication processfor the nitride semiconductor laser element according to thethirty-second embodiment shown in FIG. 165.

FIG. 170 is a perspective view for illustrating the fabrication processfor the nitride semiconductor laser element according to thethirty-second embodiment shown in FIG. 165.

FIG. 171 is a perspective view for illustrating the fabrication processfor the nitride semiconductor laser element according to thethirty-second embodiment shown in FIG. 165.

FIG. 172 is a perspective view for illustrating the fabrication processfor the nitride semiconductor laser element according to thethirty-second embodiment shown in FIG. 165.

FIG. 173 is a sectional view showing the structure of a conventionalnitride semiconductor laser element.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are now described with reference tothe drawings.

First Embodiment

First, the structure of a nitride semiconductor laser element accordingto a first embodiment is described with reference to FIGS. 1 and 2.According to this first embodiment, an n-type layer 2 of GaN having athickness of about 1 μm, an n-type cladding layer 3 ofAl_(0.08)Ga_(0.92)N having a thickness of about 1 μm and an MQW emissionlayer 4 are formed on an n-type GaN substrate 1 in this order. The MQWemission layer 4 includes an MQW active layer in which three quantumwell layers 4 c of In_(X)Ga_(1-X)N each having a thickness of about 8 nmand four barrier layers 4 b of In_(Y)Ga_(1-Y)N each having a thicknessof about 16 nm are alternately stacked. In the MQW active layeraccording to the first embodiment, the values X and Y are set to 0.13and 0.05 respectively. An n-type light guide layer 4 a ofAl_(0.01)Ga_(0.99)N having a thickness of about 0.1 μm is formed on thelower surface of the MQW active layer. Further, a p-type cap layer 4 dof Al_(0.1)Ga_(0.9)N having a thickness of about 20 nm and a p-typelight guide layer 4 e of Al_(0.01)Ga_(0.99)N having a thickness of about0.1 μm are formed on the upper surface of the MQW active layer in thisorder. The MQW emission layer 4 is an example of the “emission layer” inthe present invention, and the n-type layer 2 and the n-type claddinglayer 3 are examples of the “first nitride semiconductor layer” in thepresent invention.

A p-type cladding layer 5 of Al_(0.08)Ga_(0.92)N having a thickness ofabout 0.28 μm and a p-type contact layer 6 of Al_(0.01)Ga_(0.99)N havinga thickness of about 0.07 μm are formed on the MQW emission layer 4. Thep-type cladding layer 5 and the p-type contact layer 6 are examples ofthe “second nitride semiconductor layer” in the present invention.

According to the first embodiment, ion-implanted light absorption layers7, formed by ion-implanting carbon (C), having an implantation depth ofabout 0.32 μm are provided. Carbon is an example of the “first impurityelement” in the present invention, and the ion-implanted lightabsorption layers 7 are examples of the “light absorption layer” in thepresent invention. In this case, the peak depth of the concentration ofthe ion-implanted carbon is located in regions of the p-type claddinglayer 5 at about 0.23 μm from the upper surface of the p-type contactlayer 6. The peak concentration at this peak depth is about 1.0×10²⁰cm⁻³. In this case, the ion-implanted light absorption layers 7 containa larger number of crystal defects than the remaining regions due toimplantation of a large quantity of ions into a semiconductor. Anon-ion-implanted region (non-implanted region) forming a currentpassing region 8 is formed with a width of about 2.1 μm.

FIG. 3 is an enlarged sectional view schematically showing ion-implantedregions. The ion-implanted light absorption layers 7 indicate theion-implanted regions, and a mask layer 9 a indicates a mask layer inion implantation. FIG. 3 shows no layered structure of nitridesemiconductor layers. Referring to FIG. 3, symbol Rp denotes the peakdepth, and a solid line 7 a shows the position of the peak depth. In thenitride semiconductor laser element according to the embodiment of thepresent invention, Rp+ΔRp has been defined as the implantation depth(thickness of the ion-implanted light absorption layers 7). Symbol ΔRpdenotes the standard deviation of a range. Transverse spreading (ΔR1) ofions is caused under the mask layer 9 a in ion implantation. Assumingthat W represents the width of the mask layer 9 a in ion implantation,the width B of a region 8 a, not subjected to ion implantation, locatedunder the mask layer 9 a is expressed as B=W−2×ΔR1. Sectional viewsother than FIG. 3 illustrate no transverse spreading of ions, in orderto simplify the figures.

The ion-implanted light absorption layers 7 in the first embodimentfunction as light absorption layers due to crystal defects contained inthe ion-implanted light absorption layers 7 in a large number and alsofunction as current narrowing layers due to high resistance. In order tosufficiently perform not only current narrowing but also transverseoptical confinement in the ion-implanted light absorption layers 7, themaximum value of the impurity concentration of the ion-implanted carbonis preferably at least about 5×10¹⁹ cm⁻³. Thus, the ion-implanted lightabsorption layers 7, containing a larger number of crystal defects thanthe current passing region 8, can absorb light through the crystaldefects contained in a large number.

A p-side ohmic electrode 9 consisting of a Pt layer having a thicknessof about 1 nm, a Pd layer having a thickness of about 100 nm, an Aulayer having a thickness of about 240 nm and an Ni layer having athickness of about 240 nm in ascending order is formed on the uppersurface of the current passing region 8 of the p-type contact layer 6 ina striped (elongated) shape with an electrode width of about 2.2 μm.Insulator films 10 of SiO₂ are formed to cover the side surfaces of thep-side ohmic electrode 9 and the upper surface of the p-type contactlayer 6. A p-side pad electrode 11 consisting of a Ti layer having athickness of about 100 nm, a Pt layer having a thickness of about 150 nmand an Au layer having a thickness of about 3 μm in ascending order isformed on the insulator films 10 to be in contact with the upper surfaceof the p-side ohmic electrode 9.

An n-side ohmic electrode 12 consisting of an Al layer having athickness of about 6 nm, an Si layer having a thickness of about 2 nm,an Ni layer having a thickness of about 10 nm and an Au layer having athickness of about 100 nm successively from the side closer to the backsurface of the n-type GaN substrate 1 is formed on the back surface ofthe n-type GaN substrate 1. An n-side pad electrode 13 consisting of anNi layer having a thickness of about 10 nm and an Au layer having athickness of about 700 nm successively from the side closer to then-side ohmic electrode 12 is formed on the back surface of the n-sideohmic electrode 12.

In the nitride semiconductor laser element according to the firstembodiment, as hereinabove described, the ion-implanted light absorptionlayers 7 formed by ion-implanting carbon into the regions of the p-typecladding layer 5 and the p-type contact layer 6 formed on the MQWemission layer 4 other than the current passing region 8 are so providedthat the ion-implanted light absorption layers 7 can be formed withexcellent reproducibility due to excellent reproducibility of ionimplantation. Thus, transverse optical confinement can be controlledwith excellent reproducibility. Consequently, the yield can be improvedas compared with a conventional nitride semiconductor laser elementhaving a ridge portion.

In the nitride semiconductor laser element according to the firstembodiment, further, the ion-implanted light absorption layers 7 formedby ion implantation are so provided as hereinabove described that noirregularity or high-density crystal defects are formed on theinterfaces between the ion-implanted light absorption layers 7 and thecurrent passing region 8 dissimilarly to a conventional structure havinga ridge portion formed by etching. Thus, generation of a leakage currentresulting from crystal defects can be remarkably suppressed.

In a fabrication process for the nitride semiconductor laser elementaccording to the first embodiment, implanted ions are peaked in thep-type cladding layer 5 as described above, whereby crystal defects canbe formed in the p-type cladding layer 5 with sufficient density. Thus,the ion-implanted light absorption layers 7 having a sufficient lightabsorption effect can be formed in the p-type cladding layer 5.Consequently, the nitride semiconductor laser element has a sufficienttransverse optical confinement effect. Further, the ion-implanted lightabsorption layers 7 are formed separately from the MQW emission layer 4by a first distance of 0.03 μm in the depth direction so that the MQWemission layer 4 located under the ion-implanted light absorption layers7 has a small number of crystal defects, whereby reduction of the lifeof the element can be suppressed.

In the nitride semiconductor laser element according to the firstembodiment, as hereinabove described, the ion-implanted light absorptionlayers 7 formed by ion implantation are so provided that no conventionalprojecting ridge portion is necessary. Thus, when the element is mountedon a heat radiation base in a junction-down system from the surfacecloser to the MQW emission layer 4, the element characteristics are notdisadvantageously deteriorated due to stress applied to a projectingridge portion. Further, no such disadvantage is caused either that heatradiation characteristics are deteriorated due to reduction of a contactarea with the heat radiation base resulting from a projecting ridgeportion.

In the nitride semiconductor laser element according to the firstembodiment, as hereinabove described, the insulator films 10 are soformed on the ion-implanted light absorption layers 7 that generation ofa small leakage current can be prevented when a high current is injectedinto the element.

The fabrication process for the nitride semiconductor laser elementaccording to the first embodiment is now described with reference toFIGS. 1 to 9.

As shown in FIG. 4, the n-type layer 2 of GaN having the thickness ofabout 1 μm and the n-type cladding layer 3 of Al_(0.08)Ga_(0.92)N havingthe thickness of about 1 μm are successively formed on the n-type GaNsubstrate 1 by MOCVD (Metal Organic Chemical Vapor Deposition: metalorganic chemical vapor deposition). The MQW emission layer 4 consistingof the MQW active layer in which the n-type light guide layer 4 a ofAl_(0.01)Ga_(0.99)N having the thickness of about 0.1 μm, the threequantum well layers 4 c of In_(X)Ga_(1-X)N each having the thickness ofabout 8 nm and the four barrier layers 4 b of In_(Y)Ga_(1-Y)N eachhaving the thickness of about 16 nm are stacked, the p-type cap layer 4d of Al_(0.1)Ga_(0.9)N having the thickness of about 20 nm and thep-type light guide layer 4 e of Al_(0.01)Ga_(0.99)N having the thicknessof about 0.1 μm is formed on this n-type cladding layer 3, as shown inFIG. 2. The p-type cladding layer 5 of Al_(0.08)Ga_(0.92)N having thethickness of about 0.28 μm and the p-type contact layer 6 ofAl_(0.01)Ga_(0.99)N having the thickness of about 0.07 μm aresuccessively formed on this MQW emission layer 4. Si is added as ann-type dopant, and Mg is added as a p-type dopant.

As shown in FIG. 5, the p-side ohmic electrode 9 consisting of the Ptlayer having the thickness of about 1 nm, the Pd layer having thethickness of about 100 nm, the Au layer having the thickness of about240 nm and the Ni layer having the thickness of about 240 nm inascending order is formed on the upper surface of the p-type contactlayer 6 for forming the current passing region 8 by a lift-off method inthe striped (elongated) shape with the electrode width of about 2.2 μm.When the electrode width of the p-side ohmic electrode 9 is in the rangeof about 1 μm to about 6 μm, a current path can be sufficiently ensuredwhile transverse optical confinement can also be excellently performed.

In other words, contact areas of the p-side ohmic electrode 9 and thep-type contact layer 6 are reduced if the electrode width of the p-sideohmic electrode 9 is set to not more than about 1 μm, to increasecontact resistance. When ion implantation is performed through thisp-side ohmic electrode 9 serving as a mask, crystal defects areintroduced also in the transverse direction, as described later. Thus,this region has high resistance and hence the effective width of thecurrent passing region 8 is reduced to result in excess current density.Consequently, temperature rise is increased to cause increase of anoperating current or reduction of the element life. In an extreme case,further, there is an apprehension that no effective current path can beensured and no current can be injected into the element as a result. Ifthe electrode width of the p-side ohmic electrode 9 is rendered largerthan 6 μm, on the other hand, the width of the current passing region 8is excessively increased to excessively reduce the current density.Consequently, a threshold current may be remarkably increased. Further,the ion-implanted light absorption layers 7 are so excessively separatedfrom an emission portion of the MQW emission layer 4 that transverseoptical confinement may be insufficient. Therefore, the electrode widthof the p-side ohmic electrode 9 is preferably set in the range of about1 μm to about 6 μm.

Then, a through film 14 of SiO₂ having a thickness of about 60 nm isformed by plasma CVD to cover the overall upper surfaces of the p-sideohmic electrode 9 and the p-type contact layer 6.

As shown in FIG. 6, the p-side ohmic electrode 9 is employed as a maskfor ion-implanting a large quantity of carbon into prescribed regions ofthe p-type contact layer 6 and the p-type cladding layer 5 through thethrough film 14, thereby forming the ion-implanted light absorptionlayers 7 having the ion implantation depth (thickness) of about 0.32 μmfrom the upper surface of the p-type contact layer 6. Thus, the currentpassing region 8 having the current passing width of about 2.1 μm isformed. According to the first embodiment, carbon was ion-implantedunder conditions of ion implantation energy of about 95 keV and a doseof about 2.3×10¹⁵ cm⁻². This ion implantation was performed from adirection inclined from a direction ([0001] direction of the p-typecontact layer 6) perpendicular to the surface of the p-type contactlayer 6 by about 70 in the stripe direction of the p-side ohmicelectrode 9.

FIG. 8 shows simulation results of a carbon concentration profile in thedepth direction of the element in the case of performing ionimplantation under the ion implantation conditions (implantation energy:about 95 keV, dose: about 2.3×10¹⁵ cm⁻²) according to this firstembodiment and a crystal defect concentration profile caused in acrystal due to the ion implantation. This simulation was made withsimulation software referred to as TRIM, provided to the public byengineers of IBM corporation. Referring to FIG. 8, the peak depth Rp ofthe carbon concentration is about 0.23 μm while the carbon concentrationat this peak depth Rp is about 1.0×10²⁰ cm⁻³ in the simulation resultsaccording to the ion implantation conditions of the first embodiment.Further, the standard deviation ΔRp of this graph is about 0.1 μm.

When spreading distribution of carbon and crystal defects in a direction(transverse direction) perpendicular to the ion implantation directionwas simulated by simulation through TRIM, it has been recognized thattransverse spreading (ΔR1) of about 0.12 μm is caused as schematicallyshown in FIG. 2. Thus, according to the first embodiment, the width ofthe current passing region 8 defined by the width of the ion-implantedlight absorption layers 7 is set to a value in consideration oftransverse implantation spreading of introduced ions from the width ofthe mask layer in ion implantation. In the nitride semiconductor laserelement according to the first embodiment, the sum (about 2.3 μm) of thewidth (about 2.2 μm) of the p-side ohmic electrode 9 and the thickness(about 0.1 μm in total of the right and left portions) of the portionsof the through film 14 formed on the side surfaces of the p-side ohmicelectrode 9 corresponds to the width W of the mask layer in ionimplantation. The width (about 2.1 μm) of the current passing region 8corresponding to the width B of the non-ion-implanted region locatedunder the mask layer is obtained by subtracting about 0.2 μm, which istwice the transverse implantation spreading (ΔR1), from this width ofthe mask layer.

Referring to FIG. 8, peaks are present in the p-type cladding layer 5 inboth of the carbon concentration and the crystal defect concentrationaccording to the first embodiment. More specifically, it has beenrecognized by the simulation that the peak depth of the crystal defectconcentration distribution is shallower by about 0.02 μm than that ofthe carbon concentration distribution although this is not obvious fromFIG. 8.

FIG. 9 shows results of measurement of carbon concentration distributionaccording to SIMS (Secondary Ion Mass Spectroscopy) analysis of theelement according to the ion implantation conditions of the firstembodiment. As to measurement conditions according to SIMS analysis, Cs⁺ions were employed as primary ions while a primary ion accelerationvoltage was set to 15 kV and a primary ion current was set to 25 nA. Theprimary ions were applied by raster-scanning the primary ions in aregion of 120 by 120 μm² of a sample under these measurement conditions.At this time, C⁻ ions (secondary ions) coming out from a region of 60 μmin diameter on the sample were detected thereby measuring the carbonconcentration distribution in the depth direction. While the carbonconcentration is constant (about 2×10¹⁷ cm⁻³) on a position of at leastabout 0.6 μm in implantation depth in FIG. 9, this is the concentrationof carbon not introduced by ion implantation but originally existing ina nitride semiconductor layer formed by crystal growth. Theconcentration profile of a low-concentration region shown by a brokenline in FIG. 9 is shown by excluding the concentration (about 2×10¹⁷cm⁻³) of carbon originally contained in the nitride semiconductor layerin consideration of this.

Referring to FIG. 9, it has also been recognized that the peak of thecarbon concentration distribution is in the p-type cladding layer 5 alsoin the actual carbon concentration measurement according to SIMSanalysis, similarly to the aforementioned simulation results. The peakdepth of the carbon concentration in the measurement results accordingto this SIMS analysis was about 0.15 μm from the upper surface of thep-type contact layer 6.

As hereinabove described, the peak depth Rp of the carbon concentrationdistribution was at the level of about 0.23 μm from the upper surface ofthe p-type contact layer 6 in the simulation results according to TRIM,while the peak depth of the carbon concentration according to SIMSanalysis was at the level of about 0.15 μm from the upper surface of thep-type contact layer 6. Thus, deviation of about 0.08 μm takes placebetween the trial calculated value of the peak depth of the carbonconcentration according to TRIM and the measured value of the peak depthaccording to SIMS analysis when ion-implanting carbon according to theconditions of the first embodiment. The magnitude of this deviationvaries with the type of the implanted element and the implantationconditions. When ion-implanting silicon under conditions of implantationenergy of 110 keV and a dose of 1×10¹⁵ cm⁻², for example, a trialcalculated value of the peak depth according to TRIM is about 0.15 μm,and a measured value of the peak depth according to SIMS is about 0.10μm. Thus, a trial calculated value of the peak depth of theconcentration of the implanted impurity according to TRIM and a measuredvalue of the peak depth of the concentration of the implanted impurityaccording to SIMS are not necessarily completely coincident with eachother. On the other hand, an implanted impurity concentration profileaccording to ion implantation can attain extremely high reproducibilityso far as implantation conditions are set. Thus, it is known that aplurality of elements having similar implanted impurity concentrationprofiles can be easily obtained. Each embodiment according to thepresent invention is described with trial calculated values according tothe aforementioned TRIM in principle.

After the ion-implanted light absorption layers 7 are formed by ionimplantation as described above, the through film 14 is removed by wetetching with a hydrofluoric acid etchant. Thereafter the insulator films10 of SiO₂ having the thickness of about 200 nm are formed by plasma CVDto cover the overall upper surfaces of the p-type contact layer 6 andthe p-side ohmic electrode 9, as shown in FIG. 7. A resist film (notshown) having an opening on the upper surface of the p-side ohmicelectrode 9 is formed by photolithography. This resist film is employedas a mask for removing a portion of the insulator films 10 located onthe upper surface of the p-side ohmic electrode 9 by RIE (reactive ionetching) with CF₄ gas. Thus, the upper surface of the p-side ohmicelectrode 9 is exposed.

Finally, the p-side pad electrode 11 consisting of the Ti layer havingthe thickness of about 100 nm, the Pt layer having the thickness ofabout 150 nm and the Au layer having the thickness of about 3 μm inascending order is vacuum-evaporated onto the upper surfaces of theinsulator films 10 to be in contact with the exposed upper surface ofthe p-side ohmic electrode 9, as shown in FIG. 1. The back surface ofthe n-type GaN substrate 1 is polished into a prescribed thickness (100μm, for example), and the n-side ohmic electrode 12 consisting of the Allayer having the thickness of about 6 nm, the Si layer having thethickness of about 2 nm, the Ni layer having the thickness of about 10nm an the Au layer having the thickness of about 100 nm from the sidecloser to the back surface of the n-type GaN substrate 1 is thereafterformed on the back surface of the n-type GaN substrate 1. Further, then-side pad electrode 13 consisting of the Ni layer having the thicknessof about 10 nm and the Au layer having the thickness of about 700 nmfrom the side closer to the n-side ohmic electrode 12 is formed on then-side ohmic electrode 12, thereby completing the nitride semiconductorlaser element according to the first embodiment.

In the fabrication process for the nitride semiconductor laser elementaccording to the first embodiment, channeling of carbon can besuppressed by implanting carbon from the direction inclined by about 70from the [0001] direction of the p-type contact layer 6 as hereinabovedescribed, whereby carbon can be inhibited from deep implantation intothe element. Consequently, controllability of the implantation profilein the depth direction is increased. In particular, the current passingregion 8 provided under the p-side ohmic electrode 9 can be preventedfrom implantation of ions by performing ion implantation from thedirection inclined in the stripe direction of the p-side ohmic electrode9.

In the fabrication process for the nitride semiconductor laser elementaccording to the first embodiment, as hereinabove described, the uppersurface of the element is covered with the through film 14 before ionimplantation so that channeling of carbon can be more effectivelyprevented. Thus, carbon can be further inhibited from deep implantationinto the element, whereby controllability of the implantation profile inthe depth direction is further improved.

In the fabrication process for the nitride semiconductor laser elementaccording to the first embodiment, as hereinabove described, the p-sideohmic electrode 9 employed as the mask for ion implantation can beutilized as a contact electrode, whereby fabrication steps can besimplified.

Second Embodiment

Referring to FIG. 10, the width of a current passing region is increasedwhile no through film is formed in this second embodiment, dissimilarlyto the first embodiment. The remaining structure of the secondembodiment is similar to that of the first embodiment.

Referring to FIG. 10, an n-type layer 2, an n-type cladding layer 3, anMQW emission layer 4, a p-type cladding layer 5 and a p-type contactlayer 6 are formed on an n-type GaN substrate 1 in this order accordingto this second embodiment, similarly to the first embodiment.

According to the second embodiment, ion-implanted light absorptionlayers 17, formed by ion-implanting carbon (C), having an implantationdepth of about 0.32 μm are provided similarly to the first embodiment.The ion-implanted light absorption layers 17 are examples of the “lightabsorption layer” in the present invention, and carbon is an example ofthe “first impurity element” in the present invention. In this case, thepeak depth of the concentration of ion-implanted carbon is located inregions of the p-type cladding layer 5 at about 0.23 μm from the uppersurface of the p-type contact layer 6. The peak concentration at thispeak depth is about 1.0×10²⁰ cm⁻³. In this case, the ion-implanted lightabsorption layers 17 contain a larger number of crystal defects than theremaining regions due to implantation of a large quantity of ions into asemiconductor. A non-ion-implanted region (non-implanted region) forminga current passing region 18 is formed with a width of about 2.8 μm. Thewidth (about 2.8 μm) of the current passing region 18 in a nitridesemiconductor laser element according to this second embodiment islarger than the width (about 2.1 μm) of the current passing region 8 ofthe nitride semiconductor laser element according to the firstembodiment.

The ion-implanted light absorption layers 17 in the second embodimentfunction as light absorption layers due to crystal defects contained inthe ion-implanted light absorption layers 17 in a large number and alsofunction as current narrowing layers due to high resistance. In order tosufficiently perform not only current narrowing but also transverseoptical confinement in the ion-implanted light absorption layers 17, themaximum value of the impurity concentration of ion-implanted carbon ispreferably at least about 5×10 ¹⁹ cm⁻³. Thus, the ion-implanted lightabsorption layers 17, containing a larger number of crystal defects thanthe current passing region 18, can absorb light due to the crystaldefects contained in a large number.

A p-side ohmic electrode 19 is formed on the upper surface of thecurrent passing region 18 of the p-type contact layer 6 in a striped(elongated) shape with an electrode width of about 2.0 μm, similarly tothe first embodiment. Thus, the electrode width (about 2.0 μm) of thep-side ohmic electrode 19 is smaller than the width (about 2.8 μm) ofthe current passing region 18 in the second embodiment. Insulator films20 are formed to cover the side surfaces of the p-side ohmic electrode19 and the p-type contact layer 6. A p-side pad electrode 21 is formedon the insulator films 20 to be in contact with the upper surface of thep-side ohmic electrode 19. An n-side ohmic electrode 12 and an n-sidepad electrode 13 are formed on the back surface of the n-type GaNsubstrate 1 from the side closer to the back surface of the n-type GaNsubstrate 1. The thicknesses and compositions of the respective layers19 to 21 are similar to those of the respective layers 9 to 11 in thefirst embodiment respectively. It is known that a current injected intoa p side is generally introduced into an MQW active layer without muchdiffusing all around in a nitride semiconductor laser element easilyfalling short of p-type carrier concentration. Therefore, a currentinjected from the p-side electrode reaches the MQW active layer in thecurrent passing region 18 without much spreading in the transversedirection.

In the nitride semiconductor laser element according to the secondembodiment, as hereinabove described, light absorption in locationsimmediately under the electrodes having high emission strength can befurther suppressed by reducing the width of the p-side ohmic electrode19 beyond the interval (width of the current passing region 18) betweenthe ion-implanted light absorption layers 17. Thus, increase of athreshold current and reduction of slope efficiency (current-opticaloutput characteristics) can be suppressed.

A fabrication process for the nitride semiconductor laser elementaccording to the second embodiment is now described with reference toFIGS. 10 to 13. The fabrication process according to the secondembodiment is described with reference to a fabrication process ofincreasing the width of the current passing region 18 through anon-implanted region enlarging film while forming no through film.

First, the layers up to the p-type contact layer 6 are formed through aprocess similar to that of the first embodiment shown in FIG. 4. Asshown in FIG. 11, the p-side ohmic electrode 19 having the width ofabout 2 μm is formed on the upper surface of the p-type contact layer 6by a lift-off method in a striped shape, similarly to the firstembodiment.

Thereafter a non-implanted region enlarging film 22 of SiO₂ having athickness of about 500 nm is formed by plasma CVD to cover the overallupper surfaces of the p-side ohmic electrode 19 and the p-type contactlayer 6 according to the second embodiment. The non-implanted regionenlarging film 22 is anisotropically etched by RIE employing CF₄ gas.Thus, non-implanted region enlarging films 22 a having a width of about500 nm are formed on both side wall portions of the p-side ohmicelectrode 19 respectively, as shown in FIG. 12. Thereafter the p-sideohmic electrode 19 and the non-implanted region enlarging films 22 a areemployed as masks (width of masks: about 3 μm) for performing ionimplantation. In other words, carbon is ion-implanted under conditionsof ion implantation energy of about 80 keV and a dose of about 2.3×10¹⁵cm⁻², thereby forming the ion-implanted light absorption layer 17.Thereafter the non-implanted region enlarging films 22 a removed by wetetching with a hydrofluoric etchant.

As shown in FIG. 13, the insulator films 20 of SiO₂ having a thicknessof about 200 nm are formed by plasma CVD to cover the overall surfacesof p-type contact layer 6 and the p-side ohmic electrode 19. The uppersurface of the p-side ohmic electrode 19 is exposed by photolithographyand RIE with CF₄ gas, similarly to the first embodiment.

Finally, the p-side pad electrode 21 is formed on the insulator films 20to be in contact with the upper surface of the p-side ohmic electrode 19while the n-type GaN substrate 1 is polished into a prescribed thicknessand the n-side ohmic electrode 12 and the n-side pad electrode 13 arethereafter formed on this back surface of this n-type GaN substrate 1through a process similar to that of the first embodiment, therebycompleting the nitride semiconductor laser element according to thesecond embodiment as shown in FIG. 10.

Third Embodiment

Referring to FIG. 14, the width of a current passing region is reducedwhile no through film is formed in this third embodiment, dissimilarlyto the first embodiment. The remaining structure of the third embodimentis similar to that of the first embodiment.

Referring to FIG. 14, an n-type layer 2, an n-type cladding layer 3, anMQW emission layer 4, a p-type cladding layer 5 and a p-type contactlayer 6 are formed on an n-type GaN substrate 1 in this order accordingto this third embodiment, similarly to the first embodiment.

According to the third embodiment, ion-implanted light absorption layers27, formed by ion-implanting carbon (C), having an implantation depth ofabout 0.32 μm are provided. The ion-implanted light absorption layers 27are examples of the “light absorption layer” in the present invention,and carbon is an example of the “first impurity element” in the presentinvention. In this case, the peak depth of the concentration of theion-implanted carbon is located in regions of the p-type cladding layer5 at about 0.23 μm from the upper surface of the p-type contact layer 6.The peak concentration at this peak depth is about 1.0×10²⁰ cm⁻³. Inthis case, the ion-implanted light absorption layers 27 contain a largernumber of crystal defects than the remaining regions due to introductionof a large quantity of ions into a semiconductor. A non-ion-implantedregion (non-implanted region) forming a current passing region 28 isformed with a width of about 2.0 μm.

The ion-implanted light absorption layers 27 in the third embodimentfunction as light absorption layers due to crystal defects contained inthe ion-implanted light absorption layers 27 in a large number and alsofunction as current narrowing layers due to high resistance. In order tosufficiently perform not only current narrowing but also transverseoptical confinement in the ion-implanted light absorption layers 27, themaximum value of the impurity concentration of the ion-implanted carbonis preferably at least about 5×10⁹ cm⁻³. Thus, the ion-implanted lightabsorption layers 27, containing a larger number of crystal defects thanthe current passing region 28, can absorb light due to the crystaldefects contained in a large number.

A p-side ohmic electrode 29 is formed on the upper surface of thecurrent passing region 28 of the p-type contact layer 6 in a stripedshape with an electrode width of about 2.2 μm, similarly to the firstembodiment. According to the third embodiment, the electrode width(about 2.2 μm) of the p-side ohmic electrode 29 is substantiallyidentical to the width (about 2.0 μm) of the current passing region 28.Insulator films 30 are formed to cover the side surfaces of the p-sideohmic electrode 29 and the p-type contact layer 6. A p-side padelectrode 31 is formed on the insulator films 30 to be in contact withthe upper surface of the p-side ohmic electrode 29. An n-side ohmicelectrode 12 and an n-side pad electrode 13 are formed on the backsurface of the n-type GaN substrate 1 from the side closer to the backsurface of the n-type GaN substrate 1. The thicknesses and compositionsof the respective layers 29 to 31 are similar to those of the respectivelayers 9 to 11 of the first embodiment respectively.

In a nitride semiconductor laser element according to the thirdembodiment, effects substantially similar to those of the firstembodiment can be attained by substantially equalizing the electrodewidth of the p-side ohmic electrode 29 and the width of the currentpassing region 28 with each other, as hereinabove described. However, athreshold current is slightly increased while slope efficiency isslightly reduced as compared with the first embodiment.

A fabrication process for the nitride semiconductor laser elementaccording to the third embodiment is now described with reference toFIGS. 14 to 17. The fabrication process with no formation of a throughfilm is described with reference to the third embodiment.

First, the layers up to the p-type contact layer 6 are formed through aprocess similar to that of the first embodiment shown in FIG. 4. Asshown in FIG. 15, the p-side ohmic electrode 29 having the width ofabout 2.2 μm is formed on the upper surface of the p-type contact layer6 in the striped shape by a lift-off method, similarly to the firstembodiment.

According to the third embodiment, carbon is thereafter directlyion-implanted through the p-side ohmic electrode 29 serving as a maskwith no formation of a through film thereby forming the ion-implantedlight absorption layers 27 having the implantation depth of about 0.32μm, as shown in FIG. 16. The ion implantation in the third embodimentwas performed under conditions of ion implantation energy of about 80keV and a dose of about 2.3×10¹⁵ cm⁻².

As shown in FIG. 17, the insulator films 30 having the thickness of 200nm and consisting of SiO₂ are formed to cover the overall upper surfacesof the p-type contact layer 6 and the p-side ohmic electrode 29 byplasma CVD. The upper surface of the p-side ohmic electrode 29 isexposed by photolithography and RIE with CF₄ gas, similarly to the firstembodiment.

Finally, the p-side pad electrode 31 is formed on the p-side ohmicelectrode 29 and the insulator films 30 while the n-type GaN substrate 1is polished into a prescribed thickness and the n-side ohmic electrode12 and the n-side pad electrode 13 are thereafter formed on the backsurface of the n-type GaN substrate 1 successively from the side closerto the back surface of the n-type GaN substrate 1, thereby completingthe nitride semiconductor laser element according to the thirdembodiment shown in FIG. 14.

In the fabrication process for the nitride semiconductor laser elementaccording to the third embodiment, steps of forming and removing athrough film are unnecessary as hereinabove described, whereby thefabrication steps can be simplified.

Fourth Embodiment

Referring to FIG. 18, an example of forming no insulator films between ap-type contact layer and a p-side pad electrode in the structure of thefirst embodiment is described with reference to this fourth embodiment.The remaining structure of the fourth embodiment is similar to that ofthe first embodiment.

First, the structure of a nitride semiconductor laser element accordingto the fourth embodiment is described with reference to FIG. 18.According to this fourth embodiment, an n-type layer 2, an n-typecladding layer 3, an MQW emission layer 4, a p-type cladding layer 5 anda p-type contact layer 6 are formed on an n-type GaN substrate 1 in thisorder according to this fourth embodiment, similarly to the firstembodiment.

According to the fourth embodiment, ion-implanted light absorptionlayers 37, formed by ion-implanting carbon (C), having an implantationdepth of about 0.32 μm are provided. The ion-implanted light absorptionlayers 37 are examples of the “light absorption layer” in the presentinvention, and carbon is an example of the “first impurity element” inthe present invention. In this case, the peak depth of the concentrationof the ion-implanted carbon is located in regions of the p-type claddinglayer 5 at about 0.23 μm from the upper surface of the p-type contactlayer 6. The peak concentration at this peak depth is about 1.0×10²⁰cm⁻³. In this case, the ion-implanted light absorption layers 37 containa larger number of crystal defects than the remaining regions due tointroduction of a large quantity of ions into a semiconductor. Anon-ion-implanted region (non-implanted region) for forming a currentpassing region 38 is formed with a width of about 2.1 μm.

The ion-implanted light absorption layers 37 in the fourth embodimentfunction as light absorption layers due to the crystal defects containedin the ion-implanted light absorption layers 37 in a large number, whilefunctioning also as current narrowing layers due to high resistance. Inorder to sufficiently perform not only current narrowing but alsotransverse optical confinement in the ion-implanted light absorptionlayers 37, the maximum value of the impurity concentration of theion-implanted carbon is preferably at least about 5×10 ¹⁹ cm⁻³. Thus,the ion-implanted light absorption layers 37, containing a larger numberof crystal defects than the current passing region 38, can absorb lightthrough the crystal defects contained in a large number.

A p-side ohmic electrode 39 is formed on the upper surface of thecurrent passing region 38 of the p-type contact layer 6 in a stripedshape with an electrode width of about 2.2 μm. Further, a p-side padelectrode 40 is directly formed without through insulator films to be incontact with the upper surfaces of the p-side ohmic electrode 39 and thep-type contact layer 6. An n-side ohmic electrode 12 and an n-side padelectrode 13 are formed on the back surface of the n-type GaN substrate1 successively from the side closer to the back surface of the n-typeGaN substrate 1. The thicknesses and compositions of the respectivelayers 39 and 40 are similar to those of the respective layers 9 and 11in the first embodiment respectively.

In the nitride semiconductor laser element according to the fourthembodiment, no insulator films are formed between the p-type contactlayer 6 and the p-side pad electrode 40 as hereinabove described,whereby a step of forming insulator films can be omitted.

In the nitride semiconductor laser element according to the fourthembodiment, further, no insulator films are present between the p-typecontact layer 6 and the p-side pad electrode 40 as hereinabove describedso that effects substantially similar to those of the first embodimentcan be attained as to application in the range of a normal current,although a small leakage current may be generated through crystaldefects of the ion-implanted light absorption layers 37 when a highcurrent is applied to the element.

A fabrication process for the nitride semiconductor laser elementaccording to the fourth embodiment is similar to the fabrication processaccording to the first embodiment except that no insulator film formingstep is included.

Fifth Embodiment

Referring to FIG. 19, an example of thinly forming an insulator film ofZrO₂ on a p-type contact layer dissimilarly to the first embodiment isdescribed with reference to this fifth embodiment. The remainingstructure of the fifth embodiment is similar to that of the firstembodiment.

First, the structure of a nitride semiconductor laser element accordingto the fifth embodiment is described with reference to FIG. 19.According to this fifth embodiment, an n-type layer 2, an n-typecladding layer 3, an MQW emission layer 4, a p-type cladding layer 5 anda p-type contact layer 6 are formed on an n-type GaN substrate 1 in thisorder according to this fifth embodiment, similarly to the firstembodiment.

According to the fifth embodiment, ion-implanted light absorption layers47, formed by ion-implanting carbon (C), having an implantation depth ofabout 0.32 μm are provided similarly to the first embodiment. Theion-implanted light absorption layers 47 are examples of the “lightabsorption layer” in the present invention, and carbon is an example ofthe “first impurity element” in the present invention. In this case, thepeak depth of the concentration of the ion-implanted carbon is locatedin regions of the p-type cladding layer 5 at about 0.23 μm from theupper surface of the p-type contact layer 6. The peak concentration atthis peak depth is about 1.0×10²⁰ cm⁻³. In this case, the ion-implantedlight absorption layers 47 contain a larger number of crystal defectsthan the remaining regions due to introduction of a large quantity ofions into a semiconductor. A non-ion-implanted region (non-implantedregion) for forming a current passing region 48 is formed with a widthof about 2.1 μm.

The ion-implanted light absorption layers 47 in the fifth embodimentfunction as light absorption layers due to the crystal defects containedin the ion-implanted light absorption layers 47 in a large number, whilefunctioning also as current narrowing layers due to high resistance. Inorder to sufficiently perform not only current narrowing but alsotransverse optical confinement in the ion-implanted light absorptionlayers 47, the maximum value of the impurity concentration of theion-implanted carbon is preferably at least about 5×10¹⁹ cm⁻³. Thus, theion-implanted light absorption layers 47, containing a larger number ofcrystal defects than the current passing region 48, can absorb lightthrough the crystal defects contained in a large number.

According to the fifth embodiment, an insulator film 50 of ZrO₂ havingan opening 50 a on the upper surface of the current passing region 48 ofthe p-type contact layer 6 with a small thickness of about 50 nm isformed. The width of this opening 50 a is formed smaller than the widthof the current passing region 48. A p-side ohmic electrode 49 is formedon this insulator film 50 to be in contact with the upper surface of thep-type contact layer 6 through the opening 50 a of the insulator film 50while extending on the upper surface of the insulator film 50. A p-sidepad electrode 51 is formed on the upper surface of the p-side ohmicelectrode 49. An n-side ohmic electrode 12 and an n-side pad electrode13 are formed on the back surface of the n-type GaN substrate 1successively from the side closer to the back surface of the n-type GaNsubstrate 1.

In the nitride semiconductor laser element according to the fifthembodiment, as hereinabove described, the thickness of the insulatorfilm 50 consisting of ZrO₂ is so extremely small (50 nm) that thesurface of the p-side pad electrode 51 can be further flattened. Thus,when the element is mounted on a heat radiation base in a junction-downsystem from the surface closer to the MQW emission layer 4, the elementcharacteristics are not disadvantageously deteriorated due to stressapplied to a conventional projecting ridge portion. Further, the elementsurface is further flattened so that no such disadvantage is causedeither that heat radiation characteristics are deteriorated due toreduction of a contact area with the heat radiation base resulting froma projecting ridge portion.

A fabrication process for the nitride semiconductor laser elementaccording to the fifth embodiment is now described with reference toFIGS. 19 to 24.

First, the layers up to the p-type contact layer 6 are formed through aprocess similar to that of the first embodiment shown in FIG. 4. Asshown in FIG. 20, an ion implantation mask (not shown) of SiO₂ having athickness of about 1.0 μm is formed on the upper surface of the p-typecontact layer 6 by plasma CVD. This ion implantation mask is patternedthrough photolithography and etching, thereby forming a striped ionimplantation mask layer 52 of SiO₂ having a thickness of about 2.2 μm. Athrough film 53 of SiO₂ is formed to cover the overall upper surfaces ofthe ion implantation mask layer 52 and the p-type contact layer 6,similarly to the first embodiment.

As shown in FIG. 21, the ion implantation mask layer 52 of SiO₂ isemployed as a mask for ion-implanting carbon through the through film 53under conditions similar to those in the first embodiment, therebyforming the ion-implanted light absorption layers 47. Thereafter thethrough film 53 is removed through dry etching with CF₄ gas.

As shown in FIG. 22, an insulator film 50 b of ZrO₂ having a thicknessof about 50 nm is thereafter evaporated by EB evaporation from adirection perpendicular to the element to cover the overall uppersurfaces of the p-type contact layer 6 and the ion implantation masklayer 52 of SiO₂ according to the fifth embodiment. In this case, theinsulator film 50 b is hardly formed on the side wall portions of theion implantation mask layer 52 due to the evaporation from the directionperpendicular to the element.

As shown in FIG. 23, etching is performed with a hydrofluoric acidetchant for removing the ion implantation mask layer 52 of SiO₂ andparts of the insulator film 50 b of ZrO₂. In this case, the insulatorfilm 50 b of ZrO₂ is so hardly etched that only the parts of theinsulator film 50 b located on the side wall portions of the ionimplantation mask layer 52 are completely removed. Thus, the ionimplantation mask layer 52 of SiO₂ is completely removed after the partsof the insulator film 50 b located on the side wall portions of the ionimplantation mask layer 52 are removed. Consequently, the insulator film50 having the opening 50 a on the upper surface of the current passingregion 48 is formed as shown in FIG. 23.

Finally, the p-side ohmic electrode 49 and the p-side pad electrode 51are formed on the insulator film 50 to be in contact with the uppersurface of the p-type contact layer 6 through the opening. Further, then-type GaN substrate 1 is polished into a prescribed thickness and then-side ohmic electrode 12 and the n-side pad electrode 13 are thereafterformed on the back surface of the n-type GaN substrate 1, therebycompleting the nitride semiconductor laser element according to thefifth embodiment shown in FIG. 19. The thicknesses and compositions ofthe respective layers 51, 12 and 13 are similar to those of therespective layers 11 to 13 in the first embodiment respectively.

In the fabrication process for the nitride semiconductor laser elementaccording to the fifth embodiment, as hereinabove described, SiO₂allowing easy wet etching is employed as the material for theion-implanted mask layer 52 while ZrO₂ different from SiO₂ is employedas the material for the insulator film 50 b so that the opening 50 a canbe easily formed in the insulator film 50 b by removing the ionimplantation mask layer 52 of SiO₂ by wet etching after ionimplantation, whereby productivity can be improved.

Sixth Embodiment

Referring to FIG. 25, an example of excluding the insulator film 50 fromthe structure according to the fifth embodiment is described withreference to this sixth embodiment.

Referring to FIG. 25, an n-type layer 2, an n-type cladding layer 3, anMQW emission layer 4, a p-type cladding layer 5 and a p-type contactlayer 6 are formed on an n-type GaN substrate 1 in this order accordingto this sixth embodiment, similarly to the first embodiment.

According to the sixth embodiment, ion-implanted light absorption layers57, formed by ion-implanting carbon (C), having an implantation depth ofabout 0.32 μm are provided similarly to the first embodiment. Theion-implanted light absorption layers 57 are examples of the “lightabsorption layer” in the present invention, and carbon is an example ofthe “first impurity element” in the present invention. In this case, thepeak depth of the concentration of the ion-implanted carbon is locatedin regions of the p-type cladding layer 5 at about 0.23 μm from theupper surface of the p-type contact layer 6. The peak concentration atthis peak depth is about 1.0×10²⁰ cm⁻³. In this case, the ion-implantedlight absorption layers 57 contain a larger number of crystal defectsthan the remaining regions due to introduction of a large quantity ofions into a semiconductor. A non-ion-implanted region (non-implantedregion) for forming a current passing region 58 is formed with a widthof about 2.1 μm.

The ion-implanted light absorption layers 57 in the sixth embodimentfunction as light absorption layers due to the crystal defects containedin the ion-implanted light absorption layers 57 in a large number, whilefunctioning also as current narrowing layers due to high resistance. Inorder to sufficiently perform not only current narrowing but alsotransverse optical confinement in the ion-implanted light absorptionlayers 57, the maximum value of the impurity concentration of theion-implanted carbon is preferably at least about 5×10¹⁹ cm⁻³. Thus, theion-implanted light absorption layers 57, containing a larger number ofcrystal defects than the current passing region 58, can absorb lightthrough the crystal defects contained in a large number.

According to the sixth embodiment, a p-side ohmic electrode 59 is formedto cover the overall upper surface of the p-type contact layer 6. Ap-side pad electrode 60 is formed on this p-side ohmic electrode 59. Ann-side ohmic electrode 12 and an n-side pad electrode 13 are formed onthe back surface of the n-type GaN substrate 1 successively from theside closer to the back surface of the n-type GaN substrate 1.

In the nitride semiconductor laser element according to the sixthembodiment, as hereinabove described, the p-side ohmic electrode 59 isdirectly formed on the p-type contact layer 6 so that the surface of thep-side pad electrode 60 can be completely flattened. Thus, when theelement is mounted on a heat radiation base in a junction-down systemfrom the surface closer to the MQW emission layer 4, stress applied tothe current passing region 58 can be further reduced as compared withthe conventional ridge structure and the structures according to thefirst to fifth embodiments, whereby the element characteristics can befurther inhibited from deterioration. Further, the element surface is socompletely flattened that a contact area with the heat radiation basecan be increased, whereby more excellent heat radiation characteristicscan be attained.

In the nitride semiconductor laser element according to the sixthembodiment, the thermal conductivity of the p-side ohmic electrode 59 islarger as compared with an insulator film of SiO₂ or the like, wherebythe heat radiation characteristics of the element can be furtherimproved by directly forming the large-area p-side ohmic electrode 59 onthe p-type contact layer 6. Consequently, the element life can beimproved.

A fabrication process for the nitride semiconductor element according tothe sixth embodiment shown in FIG. 25 is now described with reference toFIGS. 25 to 28. The fabrication process according to the sixthembodiment is similar to the fabrication process according to the fifthembodiment except that no process of forming an insulator film of ZrO₂is included.

First, the layers up to the p-type contact layer 6 are formed through aprocess similar to that of the first embodiment shown in FIG. 4. Then,an ion implantation mask (not shown) of SiO₂ having a thickness of about1.0 μm is formed on the upper surface of the p-type contact layer 6 byplasma CVD. This ion implantation mask is patterned throughphotolithography and etching, thereby forming a striped ion implantationmask layer 61 having a thickness of about 2.2 μm as shown in FIG. 26. Athrough film 62 of SiO₂ is formed to cover the overall upper surfaces ofthe p-type contact layer 6 and the ion-implanted mask layer 61,similarly to the first embodiment.

As shown in FIG. 27, the ion implantation mask layer 61 of SiO₂ isemployed as a mask for ion-implanting carbon through the through film 62under conditions similar to those in the first embodiment, therebyforming the ion-implanted light absorption layers 57.

According to the sixth embodiment, the through film 62 of SiO₂ and theion implantation mask layer 61 of SiO₂ are completely removed by wetetching with a hydrofluoric acid etchant, as shown in FIG. 28.

Finally, the p-side ohmic electrode 59 and the p-side pad electrode 60are formed on the overall upper surface of the p-type contact layer 6.Further, the n-type GaN substrate 1 is polished into a prescribedthickness and the n-side ohmic electrode 12 and the n-side pad electrode13 are thereafter formed on the back surface of the n-type GaN substrate1 successively from the side closer to the back surface of the n-typeGaN substrate 1, thereby completing the nitride semiconductor laserelement according to the sixth embodiment shown in FIG. 25.

In the fabrication process for the nitride semiconductor laser elementaccording to the sixth embodiment, no insulator film 50 is formeddissimilarly to the fifth embodiment, whereby the fabrication steps canbe simplified.

Seventh Embodiment

Referring to FIG. 29, the structure of this seventh embodiment issimilar to the structure of the fifth embodiment except that the contactarea between a p-type contact layer consisting of p-typeAl_(0.01)Ga_(0.99)N and a p-side ohmic electrode is small as comparedwith the structure of the fifth embodiment.

Referring to FIG. 29, an n-type layer 2, an n-type cladding layer 3, anMQW emission layer 4, a p-type cladding layer 5 and a p-type contactlayer 6 are formed on an n-type GaN substrate 1 in this order accordingto this seventh embodiment, similarly to the first embodiment.

According to the seventh embodiment, ion-implanted light absorptionlayers 67, formed by ion-implanting carbon (C), having an implantationdepth of about 0.32 μm are provided similarly to the first embodiment.The ion-implanted light absorption layers 67 are examples of the “lightabsorption layer” in the present invention, and carbon is an example ofthe “first impurity element” in the present invention. In this case, thepeak depth of the concentration of the ion-implanted carbon is locatedin regions of the p-type contact layer 6 at about 0.23 μm from the uppersurface of the p-type contact layer 6. The peak concentration at thispeak depth is about 1.0×10²⁰ cm⁻³. In this case, the ion-implanted lightabsorption layers 67 contain a larger number of crystal defects than theremaining regions due to introduction of a large quantity of ions into asemiconductor. A non-ion-implanted region (non-implanted region) forforming a current passing region 68 is formed with a width of about 2.1μm.

The ion-implanted light absorption layers 67 in the seventh embodimentfunction as light absorption layers due to the crystal defects containedin the ion-implanted light absorption layers 67 in a large number, whilefunctioning also as current narrowing layers due to high resistance. Inorder to sufficiently perform not only current narrowing but alsotransverse optical confinement in the ion-implanted light absorptionlayers 67, the maximum value of the impurity concentration of theion-implanted carbon is preferably at least about 5×10¹⁹ cm⁻³. Thus, theion-implanted light absorption layers 67, containing a larger number ofcrystal defects than the current passing region 68, can absorb lightthrough the crystal defects contained in a large number.

According to the seventh embodiment, an insulator film 70 of ZrO₂ havingan opening 70 a (about 1.0 μm in width) on the upper surface of thecurrent passing region 68 of the p-type contact layer 6 with a smallthickness of about 50 nm is formed. The width of this opening 70 a isformed smaller than the width (about 2.2 μm) of the current passingregion 68 and smaller than the width of the opening 50 a (see FIG. 19)in the fifth embodiment. A p-side ohmic electrode 69 is formed on thisinsulator film 70 to be in contact with the upper surface of the p-typecontact layer 6 through the opening 70 a of the insulator film 70. Ap-side pad electrode 71 is formed to be in contact with the uppersurface of the p-side ohmic electrode 69. An n-side ohmic electrode 12and an n-side pad electrode 13 are formed on the back surface of then-type GaN substrate 1 successively from the side closer to the backsurface of the n-type GaN substrate 1.

In a nitride semiconductor laser element according to the seventhembodiment, as hereinabove described, the opening 70 a of the insulatorfilm 70 is rendered so small as compared with the fifth embodiment thatthe contact width between the p-side ohmic electrode 69 and the p-typecontact layer 6 can be reduced, whereby the width of current narrowingcan be further reduced as compared with the fifth embodiment.

A fabrication process for the nitride semiconductor laser elementaccording to the seventh embodiment is now described with reference toFIGS. 29 to 33. In this seventh embodiment, the fabrication processother than that of narrowly forming the opening of the insulator film ofZrO₂ on the p-type contact layer is similar to that of the fifthembodiment.

First, the layers up to the p-type contact layer 6 are formed through aprocess similar to that of the first embodiment shown in FIG. 4. Then,an ion implantation mask layer (not shown) of SiO₂ having a thickness ofabout 1 μm is formed on the upper surface of the p-type contact layer 6by plasma CVD. This ion implantation mask layer is patterned throughphotolithography and etching, thereby forming a striped ion implantationmask layer 72 of SiO₂ having a width of about 2.2 μm, as shown in FIG.30. A through film 73 of SiO₂ is formed to cover the overall surfaces ofthe p-type contact layer 6 and the ion implantation mask layer 72,similarly to the first embodiment.

As shown in FIG. 31, the ion implantation mask layer 72 of SiO₂ isemployed as a mask for ion-implanting carbon through the through film 73under conditions similar to those in the first embodiment, therebyforming the ion-implanted light absorption layers 67.

According to the seventh embodiment, the through film 73 is thereafterremoved through dry etching with CF₄ gas while isotropically etching theion implantation mask layer 72 thereby reducing the mask width of theion implantation mask layer 72 to about 1.0 μm. Thereafter an insulatorfilm 70 b of ZrO₂ having a thickness of about 50 nm is evaporated by EBevaporation from a direction perpendicular to the element to cover theoverall upper surfaces of the p-type contact layer 6 and the ionimplantation mask layer 72. In this case, the insulator film 70 b ofZrO₂ is hardly formed on the side wall portions of the ion implantationmask layer 72 of SiO₂ due to the evaporation from the directionperpendicular to the element.

As shown in FIG. 33, etching is performed with a hydrofluoric acidetchant for removing the ion implantation mask layer 72 of SiO₂ andparts of the insulator film 70 b of ZrO₂. In this case, the insulatorfilm 70 b of SiO₂ is so hardly etched that only the parts of theinsulator film 70 b located on the side wall portions of the ionimplantation mask layer 72 are completely removed. Thus, the ionimplantation mask layer 72 of SiO₂ is completely removed after the partsof the insulator film 70 b located on the side wall portions of the ionimplantation mask layer 72 are removed. Consequently, the insulator film70 having the opening 70 a (about 1.0 μm in width) on the upper surfaceof the current passing region 68 is formed as shown in FIG. 33.

Finally, the p-side ohmic electrode 69 and the p-side pad electrode 71are formed on the insulator film 70 to be in contact with the uppersurface of the p-type contact layer 6 through the opening 70 a. Further,the n-type GaN substrate 1 is polished into a prescribed thickness andthe n-side ohmic electrode 12 and the n-side pad electrode 13 arethereafter formed on the back surface of the n-type GaN substrate 1,thereby completing the nitride semiconductor laser element according tothe seventh embodiment shown in FIG. 29.

In the fabrication process for the nitride semiconductor laser elementaccording to the seventh embodiment, as hereinabove described, SiO₂allowing easy wet etching is employed as the material for theion-implanted mask layer 72 while ZrO₂ different from SiO₂ is employedas the material for the insulator film 70 b so that the opening 70 a canbe easily formed in the insulator film 70 b by removing the ionimplantation mask layer 72 of SiO₂ by wet etching after ionimplantation, whereby productivity can be improved.

Eighth Embodiment

Referring to FIG. 34, an example of forming current narrowing layers andlight absorption layers respectively by performing ion implantationtwice dissimilarly to the aforementioned first to seventh embodiments isdescribed with reference to this eighth embodiment. The remainingstructure of the eighth embodiment is similar to that of the secondembodiment.

Referring to FIG. 34, an n-type layer 2, an n-type cladding layer 3, anMQW emission layer 4, a p-type cladding layer 5 and a p-type contactlayer 6 are formed on an n-type GaN substrate 1 in this order accordingto this eighth embodiment, similarly to the first embodiment.

According to the eighth embodiment, boron (B) is ion-implanted intopartial regions of the p-type cladding layer 5 and the p-type contactlayer 6, thereby forming current narrowing layers 77 a having athickness (implantation depth) of about 0.34 μm. Boron is an example ofthe “second impurity element” in the present invention. The peak depthof the boron concentration of these current narrowing layers 77 a islocated in regions of the p-type cladding layer 5 at a depth of about0.25 μm from the upper surface of the p-type contact layer 6. The boronconcentration at this peak depth is about 1.0×10¹⁹ cm⁻³. These currentnarrowing layers 77 a perform current narrowing with respect to acurrent injected from a p side, thereby forming a current passing region78. The current passing region 78 is formed with a width of about 1.8μm.

According to the eighth embodiment, further, carbon is so ion-implantedas to form ion-implanted light absorption layers 77 b having a thickness(implantation depth) of about 0.32 μm on regions farther from the MQWemission layer 4 and the current passing region 78 than the currentnarrowing layers 77 a. The peak depth of the carbon concentration ofthese ion-implanted light absorption layers 77 b is located in thep-type cladding layer 5 at a depth of about 0.23 μm from the uppersurface of the p-type contact layer 6. The carbon concentration at thispeak depth is about 1.0×10²⁰ cm⁻³. Thus, current narrowing can beperformed in the current narrowing layers 77 a while transverse opticalconfinement can be performed in the ion-implanted light absorptionlayers 77 b. The ion-implanted light absorption layers 77 b are formedexcluding a first width (width of about 2.8 μm). Carbon ion-implanted information of the ion-implanted light absorption layers 77 b is anexample of the “first impurity elementn in the present invention, andthe ion-implanted light absorption layers 77 b are examples of the“light absorption layer” in the present invention.

A p-side ohmic electrode 79 is formed on the upper surface of thecurrent passing region 78 of the p-type contact layer 6 in a stripedshape, similarly to the second embodiment. Insulator films 80 are formedto cover the side surfaces of the p-side ohmic electrode 79 and theupper surface of the p-type contact layer 6. A p-side pad electrode 81is formed on these insulator films 80 to be in contact with the uppersurface of the p-side ohmic electrode 79. An n-side ohmic electrode 12and an n-type pad electrode 13 are formed on the back surface of then-type GaN substrate 1 successively from the side closer to the backsurface of the n-type GaN substrate 1. The thicknesses and compositionsof the respective layers 79 to 81 are similar to those of the respectivelayers 9 to 11 in the second embodiment respectively.

In a nitride semiconductor laser element according to the eighthembodiment, as hereinabove described, the ion-implanted light absorptionlayers 77 b are formed excluding the first width while the currentnarrowing layers 77 a are formed excluding the width (second width) ofthe current passing region 78, and the first width is larger than thesecond width and the region of the second width is formed in the regionof the first width. Thus, light absorption by the light absorptionlayers can be reduced while simultaneously strengthening currentnarrowing, whereby reduction of a threshold current and improvement ofslope efficiency can be attained.

In the nitride semiconductor laser element according to the eighthembodiment, further, the ion-implanted light absorption layers 77 b areformed separately from the MQW emission layer 4 by a first distance of0.03 μm while the current narrowing layers 77 a are formed separatelyfrom the MQW emission layer 4 by a second distance of 0.01 μm ashereinabove described, whereby the first distance is larger than thesecond distance. Thus, light absorption by the light absorption layerscan be reduced while simultaneously strengthening current narrowing,whereby reduction of the threshold current and improvement of the slopeefficiency can be attained.

In the nitride semiconductor laser element according to the eighthembodiment, as hereinabove described, ion implantation is set to twotypes of implantation conditions while the respective implanted regionsare so varied that the shape of the light absorption layers and theshape of the current narrowing layers can be easily controlledindependently of each other. More specifically, the interval between theion-implanted light absorption layers 77 b can be independently changedwhile keeping the width of the current passing region 78 constant at asmall width, for example. Thus, the degree of transverse opticalconfinement can be varied without remarkably changing the thresholdcurrent, whereby the horizontal divergence angle of a laser beam can becontrolled.

In the nitride semiconductor laser element according to the eighthembodiment, as hereinabove described, boron is ion-implanted at thefirst time while carbon is ion-implanted at the second time so thatintroduced elements are different from each other at the first andsecond times, whereby the concentration profiles of the introducedimpurity elements can be easily varied respectively.

In the nitride semiconductor laser element according to the eighthembodiment, as hereinabove described, a relatively light element such asboron is so ion-implanted that the current narrowing layers 77 a can beprevented from excess formation of crystal defects.

In the nitride semiconductor laser element according to the eighthembodiment, as hereinabove described, a relatively heavy element such ascarbon is so ion-implanted that crystal defects can be introduced intothe ion-implanted light absorption layers 77 b with a low dose. Thus,carbon introduced into the ion-implanted light absorption layers 77 bcan be inhibited from exerting bad influence on the characteristics ofthe element by diffusing into the MQW emission layer 4.

A fabrication process for the nitride semiconductor laser elementaccording to the eighth embodiment is now described with reference toFIGS. 34 to 38. With reference to this eighth embodiment, thefabrication process of forming the current narrowing layers and thelight absorption layers through different ion implantation stepsrespectively dissimilarly to the second embodiment is described. Theremaining structure of the fabrication process according to the eighthembodiment is similar to that of the fabrication process according tothe second embodiment.

First, the layers up to the p-type contact layer 6 are formed through aprocess similar to that of the first embodiment shown in FIG. 4. Asshown in FIG. 35, the p-side ohmic electrode 79 having the width ofabout 2 μm is formed on the upper surface of the p-type contact layer 6in the striped shape by a lift-off method, similarly to the firstembodiment.

According to the eighth embodiment, an SiO₂ film 82 a having a thicknessof about 500 nm is thereafter formed by plasma CVD to cover the overallupper surfaces of the p-side ohmic electrode 79 and the p-type contactlayer 6.

As shown in FIG. 36, the SiO₂ film 82 a is anisotropically etched by RIEemploying CF₄ gas, thereby forming non-implanted region enlarging films82 of SiO₂ having a thickness of about 500 nm on the side wall portionsof the p-side ohmic electrode 79. According to the eighth embodiment,ion implantation is performed through the p-side ohmic electrode 79 andthe non-implanted region enlarging films 82 serving as masks (width ofthe masks: about 3 μm). In other words, carbon was ion-implanted underconditions of ion implantation energy of about 80 keV and a dose ofabout 2.3×10¹⁵ cm⁻². Thus, the ion-implanted light absorption layers 77b are formed. Thereafter the non-implanted region enlarging films 82 arecompletely removed.

As shown in FIG. 37, boron is ion-implanted through the p-side ohmicelectrode 79 serving as a mask under ion implantation conditions of ionimplantation energy of about 70 keV and a dose of about 2.3×10¹⁴ cm⁻².Thus, the current narrowing layers 77 a are formed.

As shown in FIG. 38, the insulator films 80 of SiO₂ having a thicknessof about 200 nm are formed by plasma CVD to cover the side surfaces ofthe p-side ohmic electrode 79 and the upper surface of the p-typecontact layer 6. The upper surface of the p-side ohmic electrode 79 isexposed by photolithography and RIE with CF₄ gas, similarly to thesecond embodiment.

Finally, the p-side pad electrode 81 is formed on the p-side ohmicelectrode 79 and the insulator films 80 while forming the n-side ohmicelectrode 12 and the n-side pad electrode 13 on the back surface,polished into the prescribed thickness, of the n-type GaN substrate 1successively from the side closer to the back surface of the n-type GaNsubstrate 1 through a process similar to that of the second embodiment,thereby completing the nitride semiconductor laser element according tothe eighth embodiment shown in FIG. 34.

Ninth Embodiment

Referring to FIG. 39, an example of forming a p-side ohmic electrode tocover the overall upper surface of a p-type contact layer in thestructure of the eighth embodiment is described with reference to thisninth embodiment. The remaining structure of the ninth embodiment issimilar to that of the eighth embodiment.

Referring to FIG. 39, an n-type layer 2, an n-type cladding layer 3, anMQW emission layer 4, a p-type cladding layer 5 and a p-type contactlayer 6 are formed on an n-type GaN substrate 1 in this order accordingto this ninth embodiment, similarly to the first embodiment.

According to this ninth embodiment, silicon (Si) is ion-implanted intopartial regions of the p-type cladding layer 5 and the p-type contactlayer 6, thereby forming current narrowing layers 87 a having athickness (implantation depth) of about 0.34 μm. The peak depth of thesilicon concentration of these current narrowing layers 87 a is locatedin regions of the p-type cladding layer 5 at a depth of about 0.24 μmfrom the upper surface of the p-type contact layer 6. The siliconconcentration at this peak depth is about 1.0×10¹⁹ cm⁻³. The currentnarrowing layers 87 a perform current narrowing with respect to acurrent injected from a p side, thereby forming a current passing region88 having a depth of about 1.6 μm. Silicon (Si) ion-implanted information of the current narrowing layers 87 a is an example of the“second impurity element” in the present invention.

According to the ninth embodiment, further, silicon is so ion-implantedas to form ion-implanted light absorption layers 87 b having a thicknessof about 0.28 μm on regions farther from the MQW emission layer 4 andthe current passing region 88 than the current narrowing layers 87 a.The peak depth of the silicon concentration of these ion-implanted lightabsorption layers 87 b is located in the p-type cladding layer 5 at adepth of about 0.2 μm from the upper surface of the p-type contact layer6. The silicon concentration at this peak depth is about 1.0×10²⁰ cm⁻³.Thus, current narrowing can be performed in the current narrowing layers87 a while transverse optical confinement can be performed in theion-implanted light absorption layers 87 b. The ion-implanted lightabsorption layers 87 b are formed excluding a first width (width ofabout 1.8 μm). Silicon ion-implanted in formation of the ion-implantedlight absorption layers 87 b is an example of the “first impurityelement” in the present invention, and the ion-implanted lightabsorption layers 87 b are examples of the “light absorption layer” inthe present invention.

According to the ninth embodiment, a p-side ohmic electrode 89 is formedto cover the overall upper surface of the p-type contact layer 6. An ionimplantation electrode mask layer 90 having a width of about 1.8 μm isformed on the upper surface of a portion of the p-side ohmic electrode89 located on the current passing region 88 in a striped shape with athickness of about 500 nm. Insulator films 91 are formed on the sidesurfaces of the ion implantation electrode mask layer 90 and the uppersurface of the p-side ohmic electrode 89. A p-side pad electrode 92 isformed on these insulator films 91 to be in contact with the uppersurface of the ion implantation electrode mask layer 90. An n-side ohmicelectrode 12 and an n-type pad electrode 13 are formed on the backsurface of the n-type GaN substrate 1 successively from the side closerto the back surface of the n-type GaN substrate 1. The thicknesses andcompositions of the respective layers 91 and 92 are similar to those ofthe respective layers 10 and 11 in the first embodiment respectively.

In a nitride semiconductor laser element according to the ninthembodiment, as hereinabove described, the p-side ohmic electrode 89 isformed to cover the overall upper surface of the p-type contact layer 6so that the contact areas of the p-type contact layer 6 and the p-sideohmic electrode 89 can be increased, whereby contact resistance can bereduced.

A fabrication process for the nitride semiconductor laser elementaccording to the ninth embodiment is now described with reference toFIGS. 39 to 43. With reference to this ninth embodiment, the fabricationprocess of forming the current narrowing layers and the light absorptionlayers through two ion implantation steps respectively while forming thep-side ohmic electrode to cover the overall upper surface of the p-typecontact layer similarly to the eighth embodiment is described.

First, the layers up to the p-type contact layer 6 are formed through aprocess similar to that of the first embodiment shown in FIG. 4. Asshown in FIG. 40, the p-side ohmic electrode 89 consisting of a Pt layerhaving a thickness of about 1 nm and a Pd layer having a thickness ofabout 10 nm is formed to cover the overall upper surface of the p-typecontact layer 6. An Ni layer (not shown) is formed on the p-side ohmicelectrode 89 with a thickness of about 600 nm. Thereafter a resist film(not shown) having a stripe width of about 2.0 μm is formed andthereafter wet-etched with nitric acid. Thereafter this resist film isremoved thereby forming a striped ion implantation electrode mask layer90 a having a width of about 2.0 μm.

According to the ninth embodiment, the ion implantation electrode masklayer 90 a of Ni is employed as a mask for ion-implanting siliconthrough the p-side ohmic electrode 89 under ion implantation conditionsof implantation energy of about 160 keV and a dose of about 2.0×10¹⁵cm⁻² thereby forming the ion-implanted light absorption layers 87 bhaving the thickness of about 0.28 μm, as shown in FIG. 41. The ionimplantation electrode mask layer 90 a having the width of about 2.0 μmis isotropically wet-etched, thereby forming the ion implantationelectrode mask layer 90 having the width of about 1.8 μm as shown inFIG. 42. The ion implantation electrode mask layer 90 is employed as amask for ion-implanting silicon under ion implantation conditions ofimplantation energy of about 190 keV and a dose of about 2.5×10¹⁴ cm⁻²,thereby forming the current narrowing layers 87 a having the thicknessof about 0.34 μm.

As shown in FIG. 43, insulator films 91 of SiO₂ having a thickness ofabout 200 nm are formed by plasma CVD to cover the overall surfaces ofthe p-side ohmic electrode and the ion implantation electrode mask layer90. The upper surface of the ion implantation electrode mask layer 90 isexposed by photolithography and RIE with CF₄ gas.

Finally, the p-side pad electrode 92 is formed on the insulator films 91to be in contact with the upper surface of the ion implantationelectrode mask layer 90 while forming the n-side ohmic electrode 12 andthe n-side pad electrode 13 on the back surface, polished into aprescribed thickness, of the n-type GaN substrate 1 successively fromthe side closer to the back surface of the n-type GaN substrate 1through a process similar to that of the first embodiment, therebycompleting the nitride semiconductor laser element according to theninth embodiment shown in FIG. 39.

In the fabrication process for the nitride semiconductor laser elementaccording to the ninth embodiment, as hereinabove described, the overallupper surface of the element is covered with the p-side ohmic electrode89 in advance of ion implantation, whereby the introduced ions can beprevented from channeling. Thus, the introduced elements can beinhibited from deep implantation. The p-side ohmic electrode 89 is anexample of the “through film” in the present invention.

While the insulator films 91 of SiO₂ have been formed on the p-sideohmic electrode 89 in the ninth embodiment as hereinabove described, theinsulator films may not be provided. In this case, films formed on theupper surface of the p-type contact layer 6 are entirely made of metals,whereby heat radiation characteristics of the element can be furtherimproved. Consequently, the element life can be improved.

Tenth Embodiment

Referring to FIG. 44, a case of forming current narrowing layers andlight absorption layers through two ion implantation steps respectivelysimilarly to the eighth embodiment is described with reference to thistenth embodiment. In this tenth embodiment, the current narrowing layerswere formed with a low dose in order not to introduce excess crystaldefects into crystals. The remaining structure of the tenth embodimentis similar to that of the seventh embodiment.

Referring to FIG. 44, an n-type layer 2, an n-type cladding layer 3, anMQW emission layer 4, a p-type cladding layer 5 and a p-type contactlayer 6 are formed on an n-type GaN substrate 1 in this order accordingto this tenth embodiment, similarly to the first embodiment.

According to the tenth embodiment, silicon is ion-implanted into partialregions of the p-type cladding layer 5 and the p-type contact layer 6,thereby forming current narrowing layers 97 a having a thickness(implantation depth) of about 0.34 μm. Silicon is an example of the“second impurity element” in the present invention. The peak depth ofthe silicon concentration of these current narrowing layers 97 a islocated in regions of the p-type cladding layer 5 at a depth of about0.24 μm from the upper surface of the p-type contact layer 6. Thesilicon concentration at this peak depth is about 1.0×10¹⁹ cm⁻³. Thesecurrent narrowing layers 97 a perform current narrowing with respect toa current injected from a p side, thereby forming a current passingregion 98 having a width of about 1.8 μm.

According to the tenth embodiment, further, carbon is so ion-implantedas to form ion-implanted light absorption layers 97 b having a thickness(implantation depth) of about 0.32 μm on regions farther from the MQWemission layer 4 and the current passing region 98 than the currentnarrowing layers 97 a. The peak depth of the carbon concentration ofthese ion-implanted light absorption layers 97 b is located in regionsof the p-type cladding layer 5 at a depth of about 0.23 μm from theupper surface of the p-type contact layer 6. The carbon concentration atthis peak depth is about 1.0×10²⁰ cm⁻³. Thus, current narrowing can beperformed in the current narrowing layers 97 a while transverse opticalconfinement can be performed in the ion-implanted light absorptionlayers 97 b. The ion-implanted light absorption layers 97 b are formedexcluding a first width (width of about 2.1 μm). Carbon ion-implanted information of the ion-implanted light absorption layers 97 b is anexample of the “first impurity element” in the present invention, andthe ion-implanted light absorption layers 97 b are examples of the“light absorption layer” in the present invention.

An insulator film 100 of ZrO₂ having an opening on the upper surface ofthe current passing region 98 of the p-type contact layer 6 with a smallthickness of about 50 nm is formed on the upper surface of the p-typecontact layer 6, similarly to the seventh embodiment. A p-side ohmicelectrode 99 is formed on this insulator film 100 to be in contact withthe upper surface of the p-type contact layer 6 through the opening 100a of the insulator film 100. A p-side pad electrode 101 is formed to bein contact with the upper surface of the p-side ohmic electrode 99. Ann-side ohmic electrode 12 and an n-side pad electrode 13 are formed onthe back surface of the n-type GaN substrate 1 successively from theside closer to the back surface of the n-type GaN substrate 1. Thethicknesses and compositions of the respective layers 101, 12 and 13 aresimilar to those of the respective layers 11 to 13 of the firstembodiment respectively.

In a nitride semiconductor laser element according to the tenthembodiment, as hereinabove described, ion implantation is set to twotypes of implantation conditions while the respective implanted regionsare so varied that the shape of the light absorption layers and theshape of the current narrowing layers can be easily controlledindependently of each other. More specifically, the interval between theion-implanted light absorption layers 97 b can be independently changedwhile keeping the width of the current passing region 98 constant at asmall width, for example. Thus, the degree of transverse opticalconfinement can be varied without remarkably changing the thresholdcurrent, whereby the horizontal divergence angle of a laser beam can becontrolled.

In the nitride semiconductor laser element according to the tenthembodiment, as hereinabove described, silicon which is a dopant of areverse conductivity type is so ion-implanted into p-type semiconductorregions (the p-type cladding layer 5 and the p-type contact layer 6)that nitride semiconductor layers of the reverse conductivity type (ntype) can be easily formed. Thus, the current narrowing layers 97 a canbe easily formed. Consequently, the current narrowing layers 97 a can beformed with a low dose. Thus, increase of the number of crystal defectsin the current narrowing layers 97 a can be suppressed.

A fabrication process for the nitride semiconductor laser elementaccording to the ninth embodiment is now described with reference toFIGS. 44 to 46. According to the tenth embodiment, the fabricationprocess other than that of forming the current narrowing layers and thelight absorption layers through two ion implantation steps respectivelyis similar to the fabrication process according to the seventhembodiment.

First, the layers up to the p-type contact layer 6 are formed through aprocess similar to that of the first embodiment shown in FIG. 4. Asshown in FIG. 45, an ion implantation mask layer 102 having a width ofabout 2.3 μm and a through film 103 are successively formed on thep-type contact layer 6. Thereafter the ion implantation mask layer 102is employed as a mask for ion-implanting carbon under conditions similarto those in the first embodiment, thereby forming the ion-implantedlight absorption layers 97 b. Thereafter the through film 103 is removedby dry etching with CF₄.

According to the tenth embodiment, the ion implantation mask layer 102having the width of about 2.3 μm is isotropically etched thereby formingan ion implantation mask layer 102 a having a width of about 2.0 μm, asshown in FIG. 46. An insulator film 100 b of ZrO₂ having a thickness ofabout 50 nm is formed to cover the overall upper surfaces of the p-typecontact layer 6 and the ion implantation mask layer 102 a.

According to the tenth embodiment, the ion implantation mask layer 102 ais employed as a mask for ion-implanting silicon through the insulatorfilm 100 b under low-dose ion implantation conditions of implantationenergy of about 190 keV and a dose of about 2.5×10¹⁴ cm⁻². Thus, thecurrent narrowing layers 97 a having the thickness of about 0.34 μm areformed. In the current narrowing layers 97 a formed by low-dose ionimplantation, increase of the number of crystal defects is suppressed.

Thereafter etching is performed with a hydrofluoric acid etchantsimilarly to the seventh embodiment, thereby removing the ionimplantation mask layer 102 a of SiO₂ and parts of the insulator film100 b of ZrO₂. In this case, the insulator film 100 b consisting of ZrO₂is so hardly etched that only the parts of the insulator film 100 blocated on the side wall portions of the ion implantation mask layer 102a are completely removed. Thus, the ion implantation mask layer 102 a ofSiO₂ is completely removed after the parts of the insulator film 100 blocated on the side wall portions of the ion implantation mask layer 102a are removed. Consequently, the insulator film 100 having the opening100 a on the upper surface of the current passing region 98 is formed asshown in FIG. 44.

Finally, the p-side ohmic electrode 99 and the p-side pad electrode 101are formed on the insulator film 100 to be in contact with the uppersurface of the p-type contact layer 6 through the opening 100 a. Then-type GaN substrate 1 is polished into a prescribed thickness and then-side ohmic electrode 12 and the n-side pad electrode 13 are thereafterformed on the back surface of the n-type GaN substrate 1 successivelyfrom the side closer to the back surface of the n-type GaN substrate 1,thereby completing the nitride semiconductor laser element according tothe tenth embodiment shown in FIG. 44.

In the fabrication process for the nitride semiconductor laser elementaccording to the tenth embodiment, as hereinabove described, the overallsurface of the element is covered with the insulator film 100 b or thethrough film 103 in advance of ion implantation, whereby implanted ionscan be prevented from channeling. Thus, introduced elements can beinhibited from deep implantation. The insulator film 102 b and thethrough film 103 are examples of the “through film” in the presentinvention.

Eleventh Embodiment

Referring to FIG. 47, an example of forming current narrowing layers bythermal diffusion of hydrogen atoms while forming light absorptionlayers by ion implantation of silicon is described with reference tothis eleventh embodiment. In a nitride semiconductor laser elementaccording to this eleventh embodiment, the current narrowing layers areformed over an n-type cladding layer, an MQW emission layer, a p-typecladding layer and a p-type contact layer. The remaining structure ofthe eleventh embodiment is similar to that of the first embodiment.

Referring to FIG. 47, an n-type layer 2, an n-type cladding layer 3, anMQW emission layer 4, a p-type cladding layer 5 and a p-type contactlayer 6 are formed on an n-type GaN substrate 1 in this order accordingto this eleventh embodiment, similarly to the first embodiment.

According to the eleventh embodiment, current narrowing layers 107 aformed by thermally diffusing hydrogen are formed on partial regions ofthe p-type cladding layer 5 and the p-type contact layer 6. Thesecurrent narrowing layers 107 a have a thickness (diffusion regions)reaching partial upper portions of the n-type cladding layer 3 from theupper surface of the p-type contact layer 6. These current narrowinglayer 107 a perform current narrowing with respect to currents injectedfrom a p side and an n side, thereby forming a current passing region108 having a width of about 1.4 μm. Hydrogen is an example of the“second impurity element” in the present invention.

According to the eleventh embodiment, further, silicon is soion-implanted as to form ion-implanted light absorption layers 107 bhaving a thickness of about 0.34 μm on regions farther from the MQWemission layer 4 and the current passing region 108 than the currentnarrowing layers 107 a. The peak depth of the silicon concentration ofthese ion-implanted light absorption layers 107 b is located in regionsof the p-type cladding layer 5 at a depth of about 0.24 μm from theupper surface of the p-type contact layer 6. The silicon concentrationat this peak depth is about 1.0×10²⁰ cm⁻³. Thus, current narrowing canbe performed in the current narrowing layers 107 a while transverseoptical confinement can be performed in the ion-implanted lightabsorption layers 107 b. The ion-implanted light absorption layers 107 bare formed excluding a first width (width of about 1.9 μm). Theion-implanted light absorption layers 107 b are examples of the “lightabsorption layer” in the present invention, and Si is an example of the“first impurity element” in the present invention.

A p-side ohmic electrode 109 having a width of about 2.0 μm is formed onthe upper surface of the current passing region 108 of the p-typecontact layer 6 in a striped shape. Insulator films 110 are formed tocover the side surfaces of the p-side ohmic electrode 109 and the uppersurface of the p-type contact layer 6. A p-side pad electrode 111 isformed on these insulator films 110 to be in contact with the uppersurface of the p-side ohmic electrode 109. An n-side ohmic electrode 12and an n-side pad electrode 13 are formed on the back surface of then-type GaN substrate 1 successively from the side closer to the backsurface of the n-type GaN substrate 1. The thicknesses and compositionsof the respective layers 109 to 111 are similar to those of therespective layers 9 to 11 of the first embodiment respectively.

In the nitride semiconductor laser element according to the eleventhembodiment, as hereinabove described, the ion-implanted light absorptionlayers 107 b are formed separately from the MQW emission layer 4 by afirst distance of 0.01 μm in the depth direction while the currentnarrowing layers 107 a are formed in the MQW emission layer 4, wherebythe first distance is larger than a second distance. In the eleventhembodiment, the second distance defined by the interval between the MQWemission layer 4 and the current narrowing layers 107 a is zero. Thus,light absorption by the light absorption layers can be reduced whilesimultaneously strengthening current narrowing, whereby reduction of athreshold current and improvement of slope efficiency can be attained.

In the nitride semiconductor laser element according to the eleventhembodiment, as hereinabove described, the current narrowing layers 107 aare formed by thermal diffusion of hydrogen atoms while theion-implanted light absorption layers 107 b are formed by ionimplantation, whereby the current passing region 108 can be limited to anarrow range through the current narrowing layers 107 a while theion-implanted light absorption layers 107 b can be provided separatelyfrom a current path. Thus, the ion-implanted light absorption layers 107b can be inhibited from excess light absorption while the thresholdcurrent can be reduced and a horizontal divergence angle of a laser beamcan be controlled.

A fabrication process for the nitride semiconductor laser elementaccording to the eleventh embodiment is now described with reference toFIGS. 47 to 51. Referring to this eleventh embodiment, the process offorming the current narrowing layers by thermal diffusion of hydrogenatoms while forming the light absorption layers by ion implantation isdescribed. The remaining structure of the eleventh embodiment is similarto that of the first embodiment.

First, the layers up to the p-type contact layer 6 are formed through aprocess similar to that of the first embodiment shown in FIG. 4. Asshown in FIG. 48, the striped p-side ohmic electrode 109 consisting of aPt layer having a thickness of about 1 nm, a Pd layer having a thicknessof about 50 nm, an Au layer having a thickness of about 240 nm and an Nilayer having a thickness of about 240 nm in ascending order is formed onpart of the upper surface of the p-type contact layer 6 with a stripewidth of about 2.0 μm.

According to the eleventh embodiment, the p-side ohmic electrode 109 isemployed as a mask for diffusing hydrogen atoms into the element byholding the element in an NH₃ atmosphere having a substrate temperatureof about 800° C., thereby forming the current narrowing layers 107 aover the n-type cladding layer 3, the MQW emission layer 4, the p-typecladding layer 5 and the p-type contact layer 6. In this case, thehydrogen atoms diffused into the element couple with carriers of p-typesemiconductor layers for inactivating functions as acceptors. Thus, theresistance of regions containing the diffused hydrogen atoms isincreased. These hydrogen atoms isotropically diffuse in the element,whereby the width of regions not increased in resistance is smaller thanthe width (about 2.0 μm) of the p-side ohmic electrode 109 serving asthe mask. Thus, the current passing region 108 having the width of about1.4 μm is formed.

As shown in FIG. 50, a through film 113 of SiO₂ having a thickness ofabout 60 nm is formed by plasma CVD to cover the overall upper surfacesof the p-side ohmic electrode 109 and the p-type contact layer 6. Thep-side ohmic electrode 109 is employed as a mask for ion-implantingsilicon through the through film 113, thereby forming the ion-implantedlight absorption layers 107 b having the thickness (implantation depth)of about 0.34 μm. In this case, the ion implantation was performed underconditions of ion implantation energy of about 190 keV and a dose ofabout 2.5×10¹⁵ cm⁻². Thereafter the through film 113 is removed with ahydrofluoric acid etchant.

As shown in FIG. 51, the insulator films 110 of SiO₂ having a thicknessof about 200 nm are formed by plasma CVD to cover the overall surfacesof the p-side ohmic electrode 109 and the p-side ohmic electrode 109.The upper surface of the p-side electrode 109 is exposed byphotolithography and RIE with CF₄ gas, similarly to the firstembodiment.

Finally, the p-side pad electrode 111 is formed on the insulator films110 to be in contact with the upper surface of the p-side ohmicelectrode 109 through a process similar to that of the first embodiment.The n-type GaN substrate 1 is polished into a prescribed thickness andthe n-side ohmic electrode 12 and the n-side pad electrode 13 arethereafter formed on the back surface of the n-type GaN substrate 1,thereby completing the nitride semiconductor laser element according tothe eleventh embodiment shown in FIG. 47.

In the fabrication process for the nitride semiconductor laser elementaccording to the eleventh embodiment, as hereinabove described, theelement is heat-treated in an atmosphere containing hydrogen atoms fordiffusing the hydrogen atoms into p-type semiconductor regions, wherebythe current narrowing layers 107 a extending over the n-type claddinglayer 3, the MQW emission layer 4, the p-type cladding layer 5 and thep-type contact layer 6 can be easily formed. In this case, crystaldefects are so hardly introduced as compared with a case of formingcurrent blocking regions by ion implantation that reliability of theelement can be improved. In particular, the ion-implanted lightabsorption layers 107 b formed by ion implantation are formed on regionsseparated from an emission part of the MQW emission layer 4, whereby theemission part can be further effectively prevented from formation ofcrystal defects.

Twelfth Embodiment

Referring to FIG. 52, a case of forming current narrowing layers andlight absorption layers extending over an n-type cladding layer, an MQWemission layer, a p-type cladding layer and a p-type contact layer byion-implanting silicon twice respectively is described with reference tothis twelfth embodiment. The remaining structure of the twelfthembodiment is similar to that of the first embodiment.

Referring to FIG. 52, an n-type layer 2, an n-type cladding layer 3, anMQW emission layer 4, a p-type cladding layer 5 and a p-type contactlayer 6 are formed on an n-type GaN substrate 1 in this order accordingto this twelfth embodiment, similarly to the first embodiment.

According to the twelfth embodiment, silicon (Si) is ion-implanted intopartial regions of the layers from the n-type cladding layer 3 to thep-type contact layer 6 thereby forming current narrowing layers 117 bhaving a thickness (implantation depth) of about 0.73 μm over the n-typecladding layer 3, the MQW emission layer 4, the p-type cladding layer 5and the p-type contact layer 6. The peak depth of the siliconconcentration of these current narrowing layers 117 b is located inregions of the MQW emission layer 4 at a depth of about 0.55 μm from theupper surface of the p-type contact layer 6. The silicon concentrationat this peak depth is about 1.0×10¹⁹ cm⁻³. These current narrowinglayers 117 b perform current narrowing with respect to currents injectedfrom a p side and an n side, thereby forming a current passing region118 having a width of about 1.9 μm. Silicon is an example of the “secondimpurity element” in the present invention.

Further, silicon is ion-implanted again under different conditions,thereby forming ion-implanted light absorption layers 117 a having thesame width as the current narrowing layers 117 b and a thickness ofabout 0.34 μm. The peak depth of the silicon concentration of theseion-implanted light absorption layers 117 a is at a level of about 0.24μm from the upper surface of the p-type contact layer 6. The siliconconcentration at this peak depth is about 1.0×10²⁰ cm⁻³. Thus, currentnarrowing can be performed in the current narrowing layers 117 b whiletransverse optical confinement can be performed in the ion-implantedlight absorption layers 117 a. The ion-implanted light absorption layers117 a are formed excluding a first width (width of about 2.1 μm).Silicon is an example of the “first impurity element” in the presentinvention, and the ion-implanted light absorption layers 117 a areexamples of the “light absorption layer” in the present invention.

A p-side ohmic electrode 119 having a width of about 2.2 μm is formed onthe upper surface of the current passing region 118 of the p-typecontact layer 6 in a striped shape. Insulator films 120 are formed tocover the side surfaces of the p-side ohmic electrode 119 and the uppersurface of the p-type contact layer 6. A p-side pad electrode 121 isformed on these insulator films 120 to be in contact with the uppersurface of the p-side ohmic electrode 119. An n-side ohmic electrode 12and an n-type pad electrode 13 are formed on the back surface of then-type GaN substrate 1 successively from the side closer to the backsurface of the n-type GaN substrate 1. The thicknesses and compositionsof the respective layers 119 to 121 are similar to those of therespective layers 9 to 11 in the first embodiment respectively.

In a nitride semiconductor laser element according to the twelfthembodiment, as hereinabove described, ion implantation is performedunder two types of implantation conditions for changing respectiveimplanted regions (implantation depths), whereby the shape of the lightabsorption layers and the shape of the current narrowing layers can beeasily controlled independently of each other. More specifically,current narrowing can be sufficiently performed with the currentnarrowing layers 117 b, having the large thickness (implantation depth),reaching the upper surface of the p-type contact layer 6 from the n-typecladding layer 3 having relatively small light absorption whiletransverse optical confinement can be performed with the ion-implantedlight absorption layers 117 a, having a small thickness, reaching theupper surface of the p-type contact layer 6 from the p-type claddinglayer 5. Thus, current density can be increased while excess lightabsorption can be suppressed. Consequently, a threshold current can bereduced and a horizontal divergence angle of a laser beam can becontrolled.

A fabrication process for the nitride semiconductor laser elementaccording to the twelfth embodiment is now described with reference toFIGS. 52 to 56. According to this twelfth embodiment, the fabricationprocess other than that of forming the current narrowing layers and thelight absorption layers over the n-type cladding layer, the MQW emissionlayer, the p-type cladding layer and the p-type cladding layer throughtwo ion implantation steps respectively is similar to that according tothe first embodiment.

First, the layers up to the p-type contact layer 6 are formed through aprocess similar to that of the first embodiment shown in FIG. 4. Asshown in FIG. 53, the p-side ohmic electrode 119 consisting of a Ptlayer having a thickness of about 1 nm, a Pd layer having a thickness ofabout 50 nm, an Au layer having a thickness of about 240 nm and an Nilayer having a thickness of about 240 nm is formed on part of the uppersurface of the p-type contact layer 6 in a striped shape with anelectrode width of about 2.2 μm.

Thereafter a through film 122 of SiO₂ having a thickness of about 60 nmis formed by plasma CVD to cover the overall upper surfaces of thep-side ohmic electrode 119 and the p-type contact layer 6.

According to the twelfth embodiment, the p-side ohmic electrode 119 isemployed as a mask for ion-implanting silicon through the through film122 under ion implantation conditions of implantation energy of about190 keV and a dose of about 2.5×10¹⁵ cm⁻², as shown in FIG. 54. Thus,the ion-implanted light absorption layers 117 a having the thickness ofabout 0.34 μm are formed.

As shown in FIG. 55, the p-side ohmic electrode 119 is again employed asa mask for ion-implanting silicon under ion implantation conditions ofimplantation energy of about 400 keV and a dose of about 4.5×10¹⁴ cm⁻²,thereby forming the current narrowing layers 117 b having the thicknessof about 0.73 μm. Thus, the current passing region 118 having the widthof about 1.9 μm is formed. Thereafter the through film 122 is removed bywet etching.

As shown in FIG. 56, the insulator films 120 of SiO₂ having a thicknessof about 200 nm are formed by plasma CVD to cover the overall uppersurfaces of the p-side ohmic electrode 119 and the p-type contact layer6. The upper surface of the p-side ohmic electrode 119 is exposed byphotolithography and RIE with CF₄ gas, similarly to the firstembodiment.

Finally, the p-side pad electrode 121 is formed to be in contact withthe upper surface of the p-side ohmic electrode 119 through a processsimilar to that of the first embodiment. The n-type GaN substrate 1 ispolished into a prescribed thickness and the n-side ohmic electrode 12and the n-side pad electrode 13 are thereafter formed on the backsurface of this n-type GaN substrate 1, thereby completing the nitridesemiconductor laser element according to the twelfth embodiment shown inFIG. 52.

Thirteenth Embodiment

Referring to FIG. 57, an example of forming stepped ion-implanted lightabsorption layers by ion-implanting silicon through a mask of aprojecting p-side ohmic electrode having a step is described withreference to this thirteenth embodiment.

Referring to FIG. 57, an n-type layer 2, an n-type cladding layer 3, anMQW emission layer 4, a p-type cladding layer 5 and a p-type contactlayer 6 are formed on an n-type GaN substrate 1 in this order accordingto this thirteenth embodiment, similarly to the first embodiment.

According to the thirteenth embodiment, stepped ion-implanted lightabsorption layers 127 formed by ion-implanting silicon (Si) areprovided. Silicon is an example of the “first impurity element” in thepresent invention. The ion-implanted light absorption layers 127 areexamples of the “light absorption layer” in the present invention. Anon-ion-implanted region (non-implanted region) forming a currentpassing region 128 is formed stepwise with a width of about 1.4 μm inthe range up to an implantation depth (thickness) of about 0.33 μm fromthe upper surface of the p-type contact layer 6 and a width of about 1.8μm in the range up to an implantation depth of about 0.77 μm furthertherefrom. Current narrowing is performed through narrow-intervalregions of the ion-implanted light absorption layer 127 in the range upto the implantation depth (thickness) of about 0.33 μm from the uppersurface of the p-type contact layer 6. The peak depth of the siliconconcentration in these regions is located in regions of the p-typecladding layer 5 at a depth of about 0.14 μm from the upper surface ofthe p-type contact layer 6. The silicon concentration at this peak depthis about 1.0×10²⁰ cm⁻³. Further, transverse optical confinement isperformed through wide-interval regions of the ion-implanted lightabsorption layers 127 in the range from the implantation depth(thickness) of about 0.33 μm up to the implantation depth of about 0.77μm from the upper surface of the p-type contact layer 6. The peak depthof the silicon concentration in these regions is located in regions ofthe MQW emission layer 4 at a depth of about 0.59 μm from the uppersurface of the p-type contact layer 6. The silicon concentration at thispeak depth is about 1.0×10²⁰ cm⁻³.

A projecting p-side ohmic electrode 129, having a step, consisting of aPt electrode 129 a having a thickness of 140 nm with an electrode widthof about 2.2 μm and an Ni electrode 129 b having a thickness of about600 nm with an electrode width of about 1.8 μm is formed on the uppersurface of the current passing region 128 in a striped shape. Insulatorfilms 130 are formed to cover the side surfaces of the p-side ohmicelectrode 129 and the upper surface of the p-type contact layer 6. Ap-side pad electrode 131 is formed on these insulator films 130 to be incontact with the upper surface of the p-side ohmic electrode 129. Ann-side ohmic electrode 12 and an n-side pad electrode 13 are formed onthe back surface of the n-type GaN substrate 1 successively from theside closer to the back surface of the n-type GaN substrate 1.

In a nitride semiconductor laser element according to the thirteenthembodiment, as hereinabove described, the ion-implanted light absorptionlayers 127 functioning also as current narrowing layers are so formedstepwise that sufficient current narrowing can be performed through thenarrow-interval regions of the ion-implanted light absorption layers 127and proper transverse optical confinement can be performed through thewide-interval regions of the ion-implanted light absorption layers 127closer to an emission part of the MQW emission layer 4. Thus, currentdensity can be increased while excess light absorption can besuppressed. Consequently, a threshold current can be reduced and ahorizontal divergence angle of a laser beam can be controlled.

A fabrication process for the nitride semiconductor laser elementaccording to the thirteenth embodiment is now described with referenceto FIGS. 57 to 62. With reference to the thirteenth embodiment, theexample of forming the stepped ion-implanted light absorption layershaving the current narrowing function through single ion implantation byemploying a projecting mask layer having a step is described. Theremaining structure of the thirteenth embodiment is similar to that ofthe first embodiment.

First, the layers up to the p-type contact layer 6 are formed through aprocess similar to that of the first embodiment shown in FIG. 4. Then,the p-side ohmic electrode 129 consisting of the Pt electrode 129 ahaving the thickness of about 140 nm and the Ni electrode 129 b havingthe thickness of about 600 nm is formed on the upper surface of thep-type contact layer 6 by a lift-off method in the striped shape withthe electrode width of about 2.2 μm, as shown in FIG. 58.

As shown in FIG. 59, only the Ni electrode 129 b forming the upperportion of the p-side ohmic electrode 129 is isotropically wet-etchedthereby reducing only the electrode width of the Ni electrode 129 b toabout 1.8 μm. Thus, the projecting p-side ohmic electrode 129 includingthe step is formed. Thereafter a through film 132 of SiO₂ having athickness of about 10 nm is formed by plasma CVD to cover the overallupper surfaces of the p-side ohmic electrode 129 and the p-type contactlayer 6.

According to the thirteenth embodiment, the projecting p-side ohmicelectrode 129 having the step is employed as a mask for ion-implantingsilicon through the through film 132 thereby forming the steppedion-implanted light absorption layers 127, as shown in FIG. 60.According to the thirteenth embodiment, silicon is ion-implanted underion implantation conditions of ion implantation energy of about 400 keVand a dose of about 4.5×10¹⁵ cm⁻². Thus, the stepped ion-implanted lightabsorption layers 127 are formed through single ion implantation. Inthis case, the peak depth of the concentration of silicon introducedinto the narrow-interval regions of the ion-implanted light absorptionlayers 127 is located in the regions of the p-type cladding layer 5 atthe depth of about 0.14 μm from the upper surface of the p-type contactlayer 6. The silicon concentration at this peak depth is about 1.0×10²⁰cm⁻³. The peak depth of the concentration of silicon introduced into thewide-interval regions of the ion-implanted light absorption layers 127is located in the regions of the MQW emission layer 4 at the depth ofabout 0.59 μm from the upper surface of the p-type contact layer 6. Thesilicon concentration at this peak depth is about 1.0×10²⁰ cm⁻³.Thereafter the through film 132 is removed by wet etching.

As shown in FIG. 61, the insulator films 130 of SiO₂ having a thicknessof about 200 nm are formed by plasma CVD to cover the overall uppersurfaces of the p-side ohmic electrode 129 and the p-type contact layer6. The upper surface of the p-side ohmic electrode 129 is exposed byphotolithography and RIE with CF₄ gas, similarly to the firstembodiment.

Finally, the p-side pad electrode 131 is formed on the upper surfaces ofthe insulator films 130 to be in contact with the upper surface of thep-side ohmic electrode 129 as shown in FIG. 62, through a processsimilar to that of the first embodiment. The n-type GaN substrate 1 ispolished into a prescribed thickness and the n-side ohmic electrode 12and the n-side pad electrode 13 are thereafter formed on the backsurface of this n-type GaN substrate 1, thereby completing the nitridesemiconductor laser element according to the thirteenth embodiment shownin FIG. 57.

In the fabrication process for the nitride semiconductor laser elementaccording to the thirteenth embodiment, as hereinabove described, ionimplantation is performed through the mask consisting of the projectingp-side ohmic electrode 129 having the step, whereby the steppedion-implanted light absorption layers 127 consisting of regions havingdifferent implantation depths can be formed through single ionimplantation. Thus, the ion-implantation light absorption layers 127allowing individual control of the width of the current passing region128 and the quantity of light absorption can be formed through singleion implantation. Therefore, current narrowing and transverse opticalconfinement of the laser beam can be so properly set that currentdensity can be increased while excess light absorption can besuppressed. Thus, a threshold current can be reduced and a horizontaldivergence angle of the laser beam can be controlled.

Fourteenth Embodiment

Referring to FIG. 63, a example of forming ion-implanted lightabsorption layers in an n-type cladding layer by ion-implantingmagnesium (Mg) into the n-type cladding layer in advance of formation ofan MQW emission layer is described with reference to this fourteenthembodiment.

Referring to FIG. 63, an n-type layer 2, an n-type cladding layer 3, anMQW emission layer 4, a p-type cladding layer 5 and a p-type contactlayer 6 are formed on an n-type GaN substrate 1 in this order accordingto this fourteenth embodiment, similarly to the first embodiment.

According to the fourteenth embodiment, ion-implanted light absorptionlayers 137, formed by ion-implanting magnesium (Mg), having animplantation depth of about 0.65 μm are provided on partial regions ofthe n-type cladding layer 3. The ion-implanted light absorption layers137 are examples of the “light absorption layer” in the presentinvention, and magnesium is an example of the “first impurity element”in the present invention. In this case, the peak depth of theconcentration of ion-implanted magnesium is located in regions of then-type cladding layer 3 at about 0.48 μm from the upper surface of then-type cladding layer 3. The peak concentration at this peak depth isabout 1.0×10²⁰ cm⁻³. In this case, the ion-implanted light absorptionlayers 137 contain a larger number of crystal defects than the remainingregions due to implantation of a large quantity of ions into asemiconductor. A non-ion-implanted region (non-implanted region) forminga current passing region 138 is formed with a width of about 1.9 μm.

A p-side ohmic electrode 139 consisting of a Pt layer having a thicknessof about 1 nm, a Pd layer having a thickness of about 100 nm, an Aulayer having a thickness of about 240 nm and an Ni layer having athickness of about 240 nm in ascending order is formed to cover theoverall upper surface of the p-type contact layer 6. A p-side padelectrode 140 is formed on this p-side ohmic electrode 139. An n-sideohmic electrode 12 and an n-side pad electrode 13 are formed on the backsurface of the n-type GaN substrate 1 successively from the side closerto the back surface of the n-type GaN substrate 1.

In a nitride semiconductor laser element according to the fourteenthembodiment, as hereinabove described, the impurity concentration of theimplanted ions is peaked in the n-type cladding layer 3, whereby crystaldefects can be formed in the n-type cladding layer 3 with sufficientdensity. Consequently, the ion-implanted light absorption layers 137having a sufficient light absorption effect can be formed in the n-typecladding layer 3.

A fabrication process for the nitride semiconductor laser elementaccording to the fourteenth embodiment is now described with referenceto FIGS. 63 to 66. According to the fourteenth embodiment, a processother than that of forming the ion-implanted light absorption layers inthe n-type cladding layer by implanting ions into the n-type claddinglayer in advance of formation of the MQW emission layer is similar tothe fabrication process according to the sixth embodiment.

Referring to FIG. 64, the n-type layer 2 and the n-type cladding layer 3are formed on the n-type GaN substrate 1 by MOCVD in the thirteenthembodiment.

According to the fourteenth embodiment, a striped ion implantation masklayer (not shown) having a width of about 2.3 μm is formed on the uppersurface of the n-type cladding layer 3 by a lift-off method. This ionimplantation mask layer is employed as a mask for ion-implantingmagnesium, thereby forming the ion-implanted light absorption layers 137having the implantation depth (thickness) of about 0.65 μm from theupper surface of the n-type cladding layer 3 as shown in FIG. 65. Inthis case, the peak depth of the impurity concentration of theion-implanted light absorption layers 137 is located in the regions ofthe n-type cladding layer 3 at the depth of about 0.48 μm from the uppersurface of the n-type cladding layer 3. The impurity concentration atthis peak depth is about 1.0×10²⁰ cm⁻³. Thereafter the ion implantationmask layer is removed by wet etching.

As shown in FIG. 66, the MQW emission layer 4, the p-type cladding layer5 and the p-type contact layer 6 are successively formed on the n-typecladding layer 3 by MOCVD, similarly to the first embodiment. Theion-implanted light absorption layers 137 are annealed due totemperature rise in this crystal growth.

Finally, the p-side ohmic electrode 139 and the p-side pad electrode 140are formed substantially on the overall upper surface of the p-typecontact layer 6. Further, the n-type GaN substrate 1 is polished into aprescribed thickness and the n-side ohmic electrode 12 and the n-sidepad electrode 13 are thereafter formed on the back surface of the n-typeGaN substrate 1 successively from the side closer the back surface ofthe n-type GaN substrate 1, thereby completing the nitride semiconductorlaser element according to the fourteenth embodiment shown in FIG. 63.

In the fabrication process for the nitride semiconductor laser elementaccording to the fourteenth embodiment, as hereinabove described, theMQW emission layer 4 is formed after formation of the ion-implantedlight absorption layers 137, whereby the MQW emission layer 4 can beprevented from increase of the number of crystal defects following ionimplantation. Thus, reduction of the element life can be suppressed.

In the fabrication process for the nitride semiconductor laser elementaccording to the fourteenth embodiment, as hereinabove described, noions are implanted into p-type semiconductor regions (the p-typecladding layer 5 and the p-type contact layer 6), whereby reduction ofthe number of carriers resulting from crystal defects can be suppressed.This is particularly effective since it is difficult to improve carrierdensity of a p-type semiconductor region in a nitride semiconductor.Further, the p-type contact layer 6 having a small number of crystaldefects can be formed with a wide area, whereby contact resistancebetween the p-type contact layer 6 and the p-side ohmic electrode 139can be reduced.

In the fabrication process for the nitride semiconductor laser elementaccording to the fourteenth embodiment, as hereinabove described,crystal growth is performed after increasing the temperature again afterforming the ion-implanted light absorption layers 137, whereby thenumber of crystal defects in the ion-implanted light absorption layers137 can be reduced by annealing through temperature rise. Thus, thelight absorption coefficient of the ion-implanted light absorptionlayers 137 can be easily adjusted.

Fifteenth Embodiment

Referring to FIG. 67, an example of forming ion-implanted lightabsorption layers in a p-type cladding layer by implanting ions into thep-type cladding layer in advance of formation of a p-type contact layeris described with reference to this fifteenth embodiment.

Referring to FIG. 67, an n-type layer 2, an n-type cladding layer 3, anMQW emission layer 4, a p-type cladding layer 5 and a p-type contactlayer 6 are formed on an n-type GaN substrate 1 in this order accordingto this fifteenth embodiment, similarly to the first embodiment.

According to the fifteenth embodiment, ion-implanted light absorptionlayers 147, formed by ion-implanting carbon (C), having an implantationdepth of about 0.27 μm are provided in partial regions of the p-typecladding layer 5. The ion-implanted light absorption layers 147 areexamples of the “light absorption layer” in the present invention, andcarbon is an example of the “first impurity element” in the presentinvention. In this case, the peak depth of the concentration ofion-implanted carbon is located in regions of the p-type cladding layer5 at about 0.19 μm from the upper surface of the p-type cladding layer5. The peak concentration at this peak depth is about 1.0×10²⁰ cm⁻³. Inthis case, the ion-implanted light absorption layers 147 contain alarger number of crystal defects than the remaining regions due toimplantation of a large quantity of ions into a semiconductor. Anon-ion-implanted region (non-implanted region) forming a currentpassing region 148 is formed with a width of about 1.9 μm.

A p-side ohmic electrode 149 consisting of a Pt layer having a thicknessof about 1 nm, a Pd layer having a thickness of about 100 nm, an Aulayer having a thickness of about 240 nm and an Ni layer having athickness of about 240 nm in ascending order is formed to substantiallycover the overall upper surface of the p-type contact layer 6. A p-sidepad electrode 150 is formed on this p-side ohmic electrode 149. Ann-side ohmic electrode 12 and an n-side pad electrode 13 are formed onthe back surface of the n-type GaN substrate 1 successively from theside closer to the back surface of the n-type GaN substrate 1.

In a nitride semiconductor laser element according to the fifteenthembodiment, as hereinabove described, the impurity concentration of theimplanted ions is peaked in the p-type cladding layer 5, whereby crystaldefects can be formed in the p-type cladding layer 5 with sufficientdensity. Consequently, the ion-implanted light absorption layers 147having a sufficient light absorption effect can be formed in the p-typecladding layer 5.

In the nitride semiconductor laser element according to the fifteenthembodiment, as hereinabove described, no ions are implanted into the MQWemission layer 4, whereby the MQW emission layer can be prevented fromincrease of the number of crystal defects. Thus, reduction of theelement life can be suppressed.

In the nitride semiconductor laser element according to the fifteenthembodiment, as hereinabove described, no ions are implanted into thep-type contact layer 6, whereby the p-type contact layer 6 having lowcrystal defect concentration can be formed with a wide area. Thus,carrier concentration of the p-type contact layer 6 can be improvedwhile the contact areas between the p-type contact layer 6 and thep-side ohmic electrode 149 can be widened. Consequently, contactresistance can be lowered.

A fabrication process for the nitride semiconductor laser elementaccording to the fifteenth embodiment is now described with reference toFIGS. 67 to 70. According to the fifteenth embodiment, a process otherthan that of forming the ion-implanted light absorption layers in thep-type cladding layer by implanting ions into the p-type cladding layerin advance of formation of the p-type contact layer is similar to thefabrication process according to the sixth embodiment.

As shown in FIG. 68, the n-type layer 2, the n-type cladding layer 3,the MQW emission layer 4 and the p-type cladding layer 5 are formed onthe n-type GaN substrate 1 by MOCVD, similarly to the first embodiment.

According to the fifteenth embodiment, a striped ion implantation masklayer (not shown) having a width of about 2.1 μm is formed on the uppersurface of the p-type cladding layer 5 by a lift-off method. This ionimplantation mask layer is employed as a mask for ion-implanting carbon(C) thereby forming the ion-implanted light absorption layers 147 havingthe implantation depth (thickness) of about 0.27 μm from the uppersurface of the p-type cladding layer 5, as shown in FIG. 69. Accordingto the fifteenth embodiment, carbon is ion-implanted under ionimplantation conditions of ion implantation energy of about 65 keV and adose of about 2.0×10¹⁵ cm⁻². Thereafter the ion implantation mask layeris removed by wet etching.

As shown in FIG. 70, the p-type contact layer 6 is formed by MOCVD tocover the overall upper surface of the p-type cladding layer 5. Theion-implanted light absorption layers 147 are annealed due totemperature rise in this crystal growth.

Finally, the p-side ohmic electrode 149 and the p-side pad electrode 150are formed substantially on the overall upper surface of the p-typecontact layer 6. Further, the n-type GaN substrate 1 is polished into aprescribed thickness and the n-side ohmic electrode 12 and the n-sidepad electrode 13 are thereafter formed on the back surface of the n-typeGaN substrate 1 successively from the side closer the back surface ofthe n-type GaN substrate 1, thereby completing the nitride semiconductorlaser element according to the fifteenth embodiment shown in FIG. 67.

In the fabrication process for the nitride semiconductor laser elementaccording to the fifteenth embodiment, as hereinabove described, crystalgrowth for forming the p-type contact layer 6 is performed afterincreasing the temperature again after forming the ion-implanted lightabsorption layers 147, whereby the number of crystal defects in theion-implanted light absorption layers 147 can be reduced by annealingthrough temperature rise.

Sixteenth Embodiment

Referring to FIG. 71, an example of forming two types of ion-implantedlight absorption layers by separately implanting ions into an n-typecladding layer and a p-type cladding layer respectively is describedwith reference to this sixteenth embodiment.

Referring to FIG. 71, an n-type layer 2, an n-type cladding layer 3, anMQW emission layer 4, a p-type cladding layer 5 and a p-type contactlayer 6 are formed on an n-type GaN substrate 1 in this order accordingto this sixteenth embodiment, similarly to the first embodiment.

According to the sixteenth embodiment, ion-implanted light absorptionlayers 157 a, formed by ion-implanting magnesium (Mg), having animplantation depth of about 0.65 μm are provided on partial regions ofthe n-type cladding layer 3, similarly to the fourteenth embodiment. Theion-implanted light absorption layers 157 a are examples of the “lightabsorption layer” in the present invention, and magnesium is an exampleof the “first impurity element” in the present invention. In this case,the peak depth of the concentration of ion-implanted magnesium islocated in regions of the n-type cladding layer 3 at about 0.48 μm fromthe upper surface of the n-type cladding layer 3. The peak concentrationat this peak depth is about 1.0×10²⁰ cm⁻³. In this case, theion-implanted light absorption layers 157 a contain a larger number ofcrystal defects than the remaining regions due to implantation of alarge quantity of ions into a semiconductor. A non-ion-implanted region(non-implanted region) forming a current passing region 158a is formedwith a width of about 1.9 μm.

According to the sixteenth embodiment, further, ion-implanted lightabsorption layers 157 b, formed by ion-implanting carbon (C), having animplantation depth of about 0.27 μm are provided on partial regions ofthe p-type cladding layer 5, similarly to the fifteenth embodiment. Theion-implanted light absorption layers 157 b are examples of the “lightabsorption layer” in the present invention, and carbon is an example ofthe “first impurity element” in the present invention. In this case, thepeak depth of the concentration of ion-implanted carbon is located inregions of the p-type cladding layer 5 at about 0.19 μm from the uppersurface of the p-type cladding layer 5. The peak concentration at thispeak depth is about 1.0×10²⁰ cm⁻³. In this case, the ion-implanted lightabsorption layers 157 b contain a larger number of crystal defects thanthe remaining regions due to implantation of a large quantity of ionsinto a semiconductor. A non-ion-implanted region (non-implanted region)forming a current passing region 158 is formed with a width of about 1.9μm.

A p-side ohmic electrode 159 consisting of a Pt layer having a thicknessof about 1 nm, a Pd layer having a thickness of about 100 nm, an Aulayer having a thickness of about 240 nm and an Ni layer having athickness of about 240 nm in ascending order is formed to substantiallycover the overall upper surface of the p-type contact layer 6. A p-sidepad electrode 160 is formed on this p-side ohmic electrode 159. Ann-side ohmic electrode 12 and an n-side pad electrode 13 are formed onthe back surface of the n-type GaN substrate 1 successively from theside closer to the back surface of the n-type GaN substrate 1.

In a nitride semiconductor laser element according to the sixteenthembodiment, as hereinabove described, the current passing regions 158 aand 158 b are formed under and above the MQW emission layer 4respectively, whereby sufficient current confinement can be performed.

In the nitride semiconductor laser element according to the sixteenthembodiment, as hereinabove described, the ion-implanted light absorptionlayers 157 a and 157 b are formed under and above the MQW emission layer4 respectively, whereby sufficient transverse optical confinement can beperformed.

A fabrication process for the nitride semiconductor laser elementaccording to the sixteenth embodiment is now described with reference toFIGS. 71 to 76. According to this sixteenth embodiment, a fabricationprocess other than that of separately forming the ion-implanted lightabsorption layers by implanting ions into the n-type cladding layer andthe p-type cladding layer respectively is similar to the fabricationprocess according to the sixth embodiment.

Referring to FIG. 72, the n-type layer 2 and the n-type cladding layer 3are formed on the n-type GaN substrate 1 by MOCVD according to thesixteenth embodiment.

According to the sixteenth embodiment, a striped ion implantation masklayer (not shown) having a width of about 2.3 μm is formed on the uppersurface of the n-type cladding layer 3 by a lift-off method, similarlyto the fourteenth embodiment. This ion implantation mask layer isemployed as a mask for ion-implanting magnesium, thereby forming theion-implanted light absorption layers 157 a having the implantationdepth (thickness) of about 0.65 μm from the upper surface of the n-typecladding layer 3 as shown in FIG. 73. According to the sixteenthembodiment, magnesium is ion-implanted under ion implantation conditionsof ion implantation energy of about 260 keV and a dose of about 4.3×10¹⁵cm⁻². In this case, the peak depth of the impurity concentration of theion-implanted light absorption layers 157 a is located in the regions ofthe n-type cladding layer 3 at the depth of about 0.48 μm from the uppersurface of the n-type cladding layer 3. The impurity concentration atthis peak depth is about 1.0×10²⁰ cm⁻³. Thereafter the ion implantationmask layer is removed by wet etching.

As shown in FIG. 74, the MQW emission layer 4 and the p-type claddinglayer 5 are successively formed on the n-type cladding layer 3 by MOCVD,similarly to the first embodiment. The ion-implanted light absorptionlayers 157 a are annealed due to temperature rise in this crystalgrowth.

According to the sixteenth embodiment, another striped ion implantationmask layer (not shown) having a width of about 2.1 μm is formed on thecurrent passing region 148 a on the upper surface of the p-type claddinglayer 5 by a lift-off method, similarly to the fifteenth embodiment.This ion implantation mask layer is employed as a mask forion-implanting carbon (C) thereby forming the ion-implanted lightabsorption layers 157 b having the implantation depth (thickness) ofabout 0.27 μm from the upper surface of the p-type cladding layer 5, asshown in FIG. 75. According to the sixteenth embodiment, carbon ision-implanted under ion implantation conditions of ion implantationenergy of about 65 keV and a dose of about 2.0×10¹⁵ cm⁻². Thereafter theion implantation mask layer is removed by wet etching.

Then, the p-type contact layer 6 is formed on the p-type cladding layer5 by MOCVD, as shown in FIG. 76. The ion-implanted light absorptionlayers 157 a and 157 b are annealed through temperature rise in thiscrystal growth.

Finally, the p-side ohmic electrode 159 and the p-side pad electrode 160are formed substantially on the overall upper surface of the p-typecontact layer 6. Further, the n-type GaN substrate 1 is polished into aprescribed thickness and the n-side ohmic electrode 12 and the n-sidepad electrode 13 are thereafter formed on the back surface of the n-typeGaN substrate 1 successively from the side closer to the back surface ofthe n-type GaN substrate 1, thereby completing the nitride semiconductorlaser element according to the sixteenth embodiment shown in FIG. 71.

Seventeenth Embodiment

Referring to FIG. 77, an example of applying the present invention to aplanar nitride semiconductor laser element is described with referenceto this seventeenth embodiment.

First, the structure of a nitride semiconductor laser element accordingto the seventeenth embodiment is described with reference to FIG. 77.According to the seventeenth embodiment, an n-type contact layer 172 ofGaN having a thickness of about 1.0 μm, an n-type cladding layer 173 ofAl_(0.08)Ga_(0.92)N having a thickness of about 1 μm, an MQW emissionlayer 174 of InGaN, a p-type cladding layer 175 of Al_(0.08)Ga_(0.92)Nhaving a thickness of about 0.28 μm and a p-type contact layer 176 ofAl_(0.01)Ga_(0.99)N having a thickness of about 0.07 μm are formed on aninsulating sapphire substrate 171 in this order. The n-type contactlayer 172 and the n-type cladding layer 173 are examples of the “firstnitride semiconductor layer” in the present invention, and the p-typecladding layer 175 and the p-type contact layer 176 are examples of the“second nitride semiconductor layer” in the present invention.

According to the seventeenth embodiment, ion-implanted light absorptionlayers 177 a, formed by ion-implanting carbon (C), having animplantation depth of about 0.32 μm are provided excluding a first widthof about 2.1 μm on a left-side region of the sapphire substrate 171,similarly to the first embodiment. Carbon is an example of the “firstimpurity element” in the present invention, and the ion-implanted lightabsorption layers 177 a are examples of the “light absorption layer” inthe present invention. In this case, the peak depth of the concentrationof ion-implanted carbon is located in regions of the p-type claddinglayer 175 at about 0.23 μm from the upper surface of the p-type contactlayer 176. The peak concentration at this peak depth is about 1.0×10²⁰cm⁻³. In this case, the ion-implanted light absorption layers 177 acontain a larger number of crystal defects than the remaining regionsdue to implantation of a large quantity of ions into a semiconductor.

The ion-implanted light absorption layers 177 a in the seventeenthembodiment function as light absorption layers due to crystal defectscontained in the ion-implanted light absorption layers 177 a in a largenumber. In order to sufficiently perform transverse optical confinementin the ion-implanted light absorption layers 177 a, the maximum value ofthe impurity concentration of ion-implanted carbon is preferably atleast about 1×10²⁰ cm⁻³. Thus, the ion-implanted light absorption layers177 a can absorb light due to the crystal defects contained in a largenumber.

Further, current narrowing layers (high-resistance layers) 177 b, formedby ion-implanting carbon (C), having an implantation depth of about 0.76μm are provided on the left-side region of the sapphire substrate 171.In this case, the peak depth of the concentration of ion-implantedcarbon is located in regions of about 0.61 μm from the upper surface ofthe p-type contact layer 176. The peak concentration at this peak depthis about 1.0×10¹⁹ cm⁻³. A non-ion-implanted region (non-implantedregion) forming a current passing region 178 is formed with a width ofabout 1.6 μm. Carbon is an example of the “second impurity element” inthe present invention.

A p-side ohmic electrode 179 consisting of a Pt layer having a thicknessof about 1 nm, a Pd layer having a thickness of about 100 nm, an Aulayer having a thickness of about 240 nm and an Ni layer having athickness of about 240 nm in ascending order is formed on the uppersurface of the current passing region 178 on the left-side region of thep-type contact layer 176 in a striped shape. A p-side pad electrode 180is formed to substantially cover the overall upper surface of the p-sideohmic electrode 179.

An n-type inversion layer 177 c formed by inverting a p-type portion toan n type by ion-implanting a large quantity of silicon (n-type dopant)on a region reaching part of the n-type cladding layer 173 from theupper surface of the p-type contact layer 176 is provided on aright-side region of the sapphire substrate 171. This n-type inversionlayer 177 c is formed with an implantation depth (thickness) of about0.73 μm from the upper surface of the p-type contact layer 176. Siliconis an example of the “fourth impurity element” in the present invention.

An n-side ohmic electrode 181 consisting of an Al layer having athickness of about 6 nm, an Si layer having a thickness of about 2 nm,an Ni layer having a thickness of about 10 nm and an Au layer having athickness of about 100 nm in ascending order is formed to substantiallycover the overall upper surface of the n-type inversion layer 177 c. Ann-side pad electrode 182 consisting of an Ni layer having a thickness ofabout 10 nm and an Au layer having a thickness of about 700 nm is formedon this n-side ohmic electrode 181.

In the nitride semiconductor laser element according to the seventeenthembodiment, as hereinabove described, the ion-implanted light absorptionlayers 177 a and the n-type inversion layer 177 c are formed by ionimplantation so that no conventional projecting ridge portion isnecessary. Thus, when the element is mounted on a heat radiation base ina junction-down system from the surface closer to the MQW emission layer4, the element characteristics are not disadvantageously deteriorateddue to stress applied to a projecting ridge portion. Further, heatradiation characteristics are not inconveniently deteriorated due toreduction of a contact area with the heat radiation base resulting froma projecting ridge portion.

The remaining effects of the seventeenth embodiment are similar to thoseof the first embodiment.

A fabrication process for the nitride semiconductor laser elementaccording to the seventeenth embodiment is now described with referenceto FIGS. 77 to 84.

First, the n-type contact layer 172 of GaN having the thickness of about1.0 μm, the n-type cladding layer 173 of Al_(0.08)Ga_(0.92)N having thethickness of about 1.0 μm, the MQW emission layer 174 of InGaN, thep-type cladding layer 175 of Al_(0.08)Ga_(0.92)N having the thickness ofabout 0.28 μm and the p-type contact layer 176 of Al_(0.01)Ga_(0.99)Nhaving the thickness of about 0.07 μm are successively formed on thesapphire substrate 171 by MOCVD, as shown in FIG. 78.

According to the seventeenth embodiment, an SiO₂ layer (not shown)having a thickness of about 1.0 μm is formed to substantially cover theoverall upper surface of the p-type contact layer 176. A striped ionimplantation mask layer 183 having a width of about 300 μm is formed onthe left-side region by photolithography and etching with a hydrofluoricetchant, as shown in FIG. 79. As shown in FIG. 80, this ion-implantedmask layer 183 is employed as a mask for ion-implanting silicon (n-typedopant) into portions of the p-type contact layer 176, the p-typecladding layer 175, the MQW emission layer 174 and the n-type claddinglayer 173 located on the right-side region while performing lampannealing in an N₂/H₂ gas mixture atmosphere of about 1000° C. for about30 seconds, thereby forming the n-type inversion layer 177 c having theimplantation depth (thickness) of about 0.73 μm from the upper surfaceof the p-type contact layer 176.

This ion implantation was performed under conditions of ion implantationenergy of about 400 keV and a dose of about 4.3×10¹⁵ cm⁻². In this case,the peak depth of the concentration of silicon introduced into then-type inversion layer 177 c is at a level of about 0.55 μm from theupper surface of the p-type contact layer 176. The silicon concentrationat this peak depth is about 1.0×10²⁰ cm⁻³. Thereafter the ionimplantation mask layer 183 is removed by wet etching with ahydrofluoric acid etchant.

Then, another SiO₂ layer (not shown) having a thickness of about 1.0 μmis formed on the overall upper surfaces of the n-type contact layer 176and the n-type inversion layer 177 c. As shown in FIG. 81, striped ionimplantation masks 184 a and 184 b of SiO₂ are formed on the overallupper surface of the n-type inversion region 177 c on the right-sideregion and the portion of the p-type contact layer 176 located on thecurrent passing region 178 of the left-side region respectively byphotolithography and etching. In this case, the ion implantation masklayer 184 b on the upper surface of the current passing region 178 has awidth of about 2.2 μm. A through film 185 of SiO₂ having a thickness ofabout 60 nm is formed to cover the overall upper surfaces of the ionimplantation mask layer 184 a, the ion implantation mask layer 184 b andthe p-type contact layer 176.

As shown in FIG. 82, the ion implantation mask layers 184 a and 184 bare employed as masks for ion-implanting carbon through the through film185, thereby forming the ion-implanted light absorption layers 177 ahaving the implantation depth (thickness) of about 0.32 μm from theupper surface of the p-type contact layer 176. According to theseventeenth embodiment, carbon is ion-implanted under ion implantationconditions of ion implantation energy of about 95 keV and a dose ofabout 2.3×10¹⁵ cm⁻². In this case, the peak depth of the impurityconcentration of the ion-implanted light absorption layers 177 a islocated in regions of the p-type cladding layer 175 at a depth of about0.23 μm from the upper surface of the p-type contact layer 176. The peakconcentration at this peak depth is about 1.0×10²⁰ cm⁻³. Thereafter thethrough film 185 is removed by wet etching with a hydrofluoric acidetchant.

As shown in FIG. 83, the ion implantation mask layers 184 a and 184 bare selectively etched by about 0.15 μm as to transverse single sides.Thus, an ion implantation mask layer 184 d having a width of about 2.0μm is formed. The ion implantation mask layers 184 c an 184 d areemployed as masks for ion-implanting carbon, thereby forming the currentnarrowing layers (high-resistance layers) 177 b having the implantationdepth of about 0.76 μm from the upper surface of the p-type contactlayer 176. According to the seventeenth embodiment, ion implantation isperformed under ion implantation conditions of ion implantation energyof about 230 keV and a dose of about 3.5×10¹⁴ cm⁻². In this case, thepeak depth of the carbon concentration of the current narrowing layers177 b is located in regions of about 0.61 μm from the upper surface ofthe p-type contact layer 176. The carbon concentration at this peakdepth is about 1.0×10¹⁹ cm⁻³. Thereafter the ion implantation masklayers 184 c and 184 d are removed by wet etching with a hydrofluoricacid etchant.

As shown in FIG. 84, the p-side ohmic electrode 179 consisting of the Ptlayer having the thickness of about 1 nm, the Pd layer having thethickness of about 100 nm, the Au layer having the thickness of about240 nm and the Ni layer having the thickness of about 240 nm inascending order is formed on the upper surface of the region of thep-type contact layer 176 (left-side region) forming the current passingregion 178 in the striped shape by a lift-off method. Further, then-side ohmic electrode 181 consisting of the Al layer having thethickness of about 6 nm, the Si layer having the thickness of about 2nm, the Ni layer having the thickness of about 10 nm and the Au layerhaving the thickness of about 100 nm in ascending order is formed on then-type inversion layer 177 c (right-side region) in a striped shape bythe lift-off method.

Finally, the p-side pad electrode 180 and the n-side pad electrode 182are formed to be in contact with the upper surfaces of the p-side ohmicelectrode 179 and the n-side ohmic electrode 181 respectively, therebycompleting the nitride semiconductor laser element according to theseventeenth embodiment shown in FIG. 77.

In the fabrication process for the nitride semiconductor laser elementaccording to the seventeenth embodiment, as hereinabove described,p-type regions and n-type regions can be formed in the samesemiconductor layers by performing heat treatment after ion-implanting adopant having a reverse conductivity (n type) to p-type semiconductorlayers in a large quantity.

In the fabrication process for the nitride semiconductor laser elementaccording to the seventeenth embodiment, as hereinabove described, p-nregions can be electrically isolated from each other through the currentnarrowing layers (high-resistance layers) 177 b formed by ion-implantingcarbon, whereby a plurality of elements can be easily integrated in thesame substrate. Carbon, which is the “second impurity element” in thepresent invention, is also the “third impurity element” in the presentinvention. The current narrowing layers 177 b are examples of the“electric isolation region” in the present invention. Consequently,integration of a plurality of nitride semiconductor laser elements orintegration of an electronic device such as a transistor and a nitridesemiconductor laser element can be easily performed.

In the fabrication process for the nitride semiconductor laser elementaccording to the seventeenth embodiment, as hereinabove described, noformation of a ridge portion requiring strict etching is necessary,whereby the yield can be improved.

Eighteenth Embodiment

Referring to FIG. 85, an example of integrating a plurality of nitridesemiconductor laser elements while locating concentration peaks ofimplanted ions in MQW emission layers is described with reference tothis eighteenth embodiment.

Referring to FIG. 85, an n-type layer 2, an n-type cladding layer 3, anMQW emission layer 4, a p-type cladding layer 5 and a p-type contactlayer 6 are formed on an n-type GaN substrate 1 in this order accordingto this eighteenth embodiment, similarly to the first embodiment.

According to the eighteenth embodiment, ion-implanted light absorptionlayers 187, formed by ion-implanting carbon (C), having an implantationdepth of about 0.61 μm are provided on partial regions of the n-typecladding layer 3, the MQW emission layer 4, the p-type cladding layer 5and the p-type contact layer 6. Carbon is an example of the “firstimpurity element” in the present invention, and the ion-implanted lightabsorption layers 187 are examples of the “light absorption layer” inthe present invention. In this case, the peak depth of the concentrationof ion-implanted carbon is located in regions of the MQW emission layer4 at about 0.61 μm from the upper surface of the p-type contact layer 6.The peak concentration at this peak depth is about 1.0×10¹⁸ cm⁻³ toabout 1.0×10¹⁹ cm⁻³. In this case, the ion-implanted light absorptionlayers 187 contain a larger number of crystal defects than the remainingregions due to implantation of a large quantity of ions into asemiconductor. These ion-implanted light absorption layers 187 form twotypes of emission regions. Non-ion-implanted regions (non-implantedregions) forming current passing regions 188 are formed with a width ofabout 2.6 μm.

Thus, the concentration of implanted carbon reaches the maximum valuesin the MQW emission layer 4 according to the eighteenth embodiment,whereby crystal defect concentration is maximized in the MQW emissionlayer 4 while the light absorption coefficient is also maximized in theMQW emission layer 4.

P-side ohmic electrodes 189 are formed on the upper surfaces of thecurrent passing regions 188 of the p-type contact layer 6 with anelectrode width of about 2.9 μm in a striped shape, similarly to thefirst embodiment. Insulator films 190 are formed to cover the sidesurfaces of the p-side ohmic electrodes 189 and the p-type contact layer6. P-side pad electrodes 191 are formed on the insulator films 190 to bein contact with the upper surfaces of the p-side ohmic electrodes 189.An n-side ohmic electrode 12 and an n-side pad electrode 13 are formedon the back surface of the n-type GaN substrate 1 successively from theside closer to the back surface of the n-type GaN substrate 1. Thethicknesses and compositions of the respective layers 189 to 191 aresimilar to those of the respective layers 9 to 11 of the firstembodiment respectively.

In a nitride semiconductor laser element according to the eighteenthembodiment, as hereinabove described, the carbon concentration reachesthe maximum value in the MQW emission layer 4 while the light absorptioncoefficient is also maximized in the MQW emission layer 4, wherebystrong complex refractive index difference can be formed in the in-planedirection of the MQW emission layer 4. Thus, transverse opticalconfinement can be excellently performed also through ion implantationwith a small dose.

In the nitride semiconductor laser element according to the eighteenthembodiment, as hereinabove described, the ion-implanted light absorptionlayers 187 are so increased in resistance that the MQW emission layer 4and p-type semiconductor layers of each element can be electricallyisolated from those of another element adjacent thereto in the samesubstrate when a plurality of elements are formed in the same substrate.Thus, a plurality of semiconductor laser elements can be easilyintegrated in the same substrate. The ion-implanted light absorptionlayers 187 are also examples of the “electric isolation region” in thepresent invention. Carbon, which is the “first impurity element” in thepresent invention, is also the “third impurity element” in the presentinvention.

A fabrication process for the nitride semiconductor laser elementaccording to the eighteenth embodiment is now described with referenceto FIGS. 85 to 87. With reference to the fabrication process accordingto the eighteenth embodiment, a fabrication process of locatingconcentration peaks of implanted ions in the MQW emission layer whileforming a plurality of emission regions in the same substrate isdescribed.

First, the layers up to the p-type contact layer 6 are formed through aprocess similar to that of the first embodiment show in FIG. 4. As shownin FIG. 86, the two p-side ohmic electrodes 189 having the width ofabout 2.9 μm are formed on the upper surface of the p-type contact layer6 in the striped shape at a prescribed interval by a lift-off method,similarly to the first embodiment. A through film 192 of SiO₂ having athickness of about 60 nm is formed by plasma CVD to cover the overallupper surfaces of the p-side ohmic electrodes 189 and the p-type contactlayer 6.

As shown in FIG. 87, the p-side ohmic electrodes 189 are employed asmasks for ion-implanting carbon through the through film 192 therebyforming the ion-implanted light absorption layers 187 having animplantation depth (thickness) of about 0.75 μm from the upper surfaceof the p-type contact layer 6. According to the eighteenth embodiment,carbon is ion-implanted under ion implantation conditions of ionimplantation energy of about 250 keV and a dose of about 3.5×10¹³ cm⁻²to 3.5×10¹⁴ cm⁻². Thus, the ion-implanted light absorption layers 187having the carbon concentration maximized in the MQW emission layer 4are formed. Thereafter the through film 192 is removed by wet etchingwith a hydrofluoric acid etchant.

The insulator films 190 of SiO₂ having a thickness of about 200 nm areformed by plasma CVD to cover the overall upper surfaces of the p-typecontact layer 6 and the p-side ohmic electrodes 189. The upper surfacesof the p-side ohmic electrodes 189 are exposed by photolithography andRIE with CF₄ gas, similarly to the first embodiment.

Finally, the p-side pad electrodes 191 are formed on the insulator films190 to be in contact with the exposed upper surfaces of the p-side ohmicelectrodes 189 through a process similar to that of the firstembodiment. Further, the n-side ohmic electrode 12 and the n-side padelectrode 13 are formed on the back surface, polished into a prescribedthickness, of the n-type GaN substrate 1 from the side closer to theback surface of the n-type GaN substrate 1, thereby completing thenitride semiconductor laser element according to the eighteenthembodiment shown in FIG. 85.

Nineteenth Embodiment

Referring to FIG. 88, an example of forming ion-implanted lightabsorption layers and current narrowing layers by carrying out aplurality of ion implantation steps with phosphorus (P) and carbon (C)while carrying out the respective ion implantation steps from differentangles is described with reference to this nineteenth embodiment. Theremaining structure of the nineteenth embodiment is similar to that ofthe first embodiment.

Referring to FIG. 88, an n-type layer 2, an n-type cladding layer 3, anMQW emission layer 4, a p-type cladding layer 5 and a p-type contactlayer 6 are formed on an n-type GaN substrate 1 in this order accordingto this nineteenth embodiment, similarly to the first embodiment.

According to the nineteenth embodiment, ion-implanted light absorptionlayers 197 a, formed by ion-implanting phosphorus (P), having animplantation depth of about 0.32 μm are provided on partial regions ofthe p-type cladding layer 5 and the p-type contact layer 6 excluding afirst width of about 2.8 μm. Phosphorus is an example of the “firstimpurity element” in the present invention, and the ion-implanted lightabsorption layers 197 a are examples of the “light absorption layer” inthe present invention. In this case, the peak depth of the concentrationof ion-implanted phosphorus is located in regions of the p-type claddinglayer 5 at a depth of about 0.22 μm from the upper surface of the p-typecontact layer 6. The phosphorus concentration at this peak depth isabout 1.0×10²⁰ cm⁻³.

Current narrowing layers 197 b, formed by ion-implanting carbon (C),having an implantation depth of about 0.28 μm are provided on otherpartial regions of the p-type cladding layer 5 and the p-type contactlayer 6 inside the ion-implanted light absorption layers 197 a. Carbonis an example of the “second impurity element” in the present invention.In this case, the peak depth of the concentration of ion-implantedcarbon is located in regions of the p-type cladding layer 5 at a depthof about 0.2 μm from the upper surface of the p-type contact layer 6.The carbon concentration at this peak depth is about 1.0×10¹⁹ cm⁻³. Thecurrent narrowing layers 197 b perform current narrowing with respect toa current injected from a p side, thereby forming an inverse-trapezoidalcurrent passing region 198 having a width inclinatorily changed in therange of about 2.5 μm to about 2.0 μm.

A p-side ohmic electrode 199 is formed on the upper surface of thecurrent passing region 198 of the p-type contact layer 6 with anelectrode width of about 2.9 μm in a striped shape, similarly to thefirst embodiment. Insulator films 200 are formed to cover the sidesurfaces of the p-side ohmic electrode 199 and the p-type contact layer6. A p-side pad electrode 201 is formed on the insulator films 200 to bein contact with the upper surface of the p-side ohmic electrode 199. Ann-side ohmic electrode 12 and an n-side pad electrode 13 are formed onthe back surface of the n-type GaN substrate 1 from the side closer tothe back surface of the n-type GaN substrate 1. The thicknesses andcompositions of the respective layers 199 to 201 are similar to those ofthe respective layers 9 to 11 in the first embodiment respectively.

A fabrication process for a nitride semiconductor laser elementaccording to the nineteenth embodiment is now described with referenceto FIGS. 88 to 92.

First, the layers up to the p-type contact layer 6 are formed through aprocess similar to that of the first embodiment shown in FIG. 4. Then,the p-side ohmic electrode 199 is formed on the upper surface of thep-type contact layer 6 with the electrode width of about 2.9 μm in thestriped shape by a lift-off method, as shown in FIG. 89. A through film202 of SiO₂ having a thickness of about 60 nm is formed by plasma CVD tocover the overall upper surfaces of the p-side ohmic electrode 199 andthe p-type contact layer 6.

According to the nineteenth embodiment, carbon is ion-implanted from adirection inclined at a prescribed angle about the stripe direction ofthe p-side ohmic electrode 199 from a direction perpendicular to thep-side ohmic electrode 199, as shown in FIG. 90. More specifically, thep-side ohmic electrode 199 is employed as a mask for performing firstion implantation from an angle inclined by about 30° clockwise from thedirection perpendicular to the p-type contact layer 6 ([0001] directionof the p-type contact layer 6) in a plane perpendicular to the stripedirection of the p-side ohmic electrode 199 through the through film202. Thus, high-resistance layers 197 c having an implantation depth(thickness) of about 0.28 μm from the upper surface of the p-typecontact layer 6 are formed. In the first ion implantation according tothe nineteenth embodiment, carbon is ion-implanted under ionimplantation conditions of ion implantation energy of about 95 keV and adose of about 2.3×10¹⁴ cm⁻².

Then, second ion implantation is performed from an angle inclined byabout 30° anticlockwise from the direction perpendicular to the p-typecontact layer 6 ([0001] direction of the p-type contact layer 6) in theplane perpendicular to the stripe direction of the p-side ohmicelectrode 199. Thus, high-resistance layers 197 d having an implantationdepth (thickness) of about 0.28 μm from the upper surface of the p-typecontact layer 6 are formed, as shown in FIG. 91. Second ion implantationconditions according to the nineteenth embodiment are similar to thefirst ion implantation conditions.

Further, phosphorus was ion-implanted from a direction inclined by about70 in the stripe direction of the p-side ohmic electrode 199 from thedirection perpendicular to the p-type contact layer 6, as shown in FIG.92. In this third ion implantation, phosphorus is ion-implanted underion implantation conditions of ion implantation energy of about 200 keVand a dose of about 2.5×10¹⁵ cm⁻². Thus, regions formed by the first tothird ion implantation steps overlap with each other, thereby formingthe current narrowing layers 197 b and the ion-implanted lightabsorption layers 197 a as shown in FIG. 92.

Thereafter the through film 202 is removed by wet etching with ahydrofluoric etchant. The insulator films 200 of SiO₂ having a thicknessof about 200 nm are formed by plasma CVD to cover the overall uppersurfaces of the p-type contact layer 6 and the p-side ohmic electrode199, as shown in FIG. 88. The upper surface of the p-side ohmicelectrode 199 is by photolithography and RIE with CF₄ gas, similarly tothe first embodiment.

Finally, the p-side pad electrode 201 is formed on the insulator films200 to be in contact with the exposed upper surface of the p-side ohmicelectrode 199 through a process similar to that of the first embodiment.Further, the n-side ohmic electrode 12 and the n-side pad electrode 13are formed on the back surface, polished into a prescribed thickness, ofthe n-type GaN substrate 1 from the side closer to the back surface ofthe n-type GaN substrate 1, thereby completing the nitride semiconductorlaser element according to the nineteenth embodiment shown in FIG. 88.

In the fabrication process for the nitride semiconductor laser elementaccording to the nineteenth embodiment, as hereinabove described, thewidth of the current passing region 198 can be easily rendered smallerthan the width of the p-side ohmic electrode 199 serving as the mask byperforming ion implantation a plurality of times while varying the ionimplantation angle. Thus, sufficient current narrowing can be performedwithout carrying out a complicated step of forming a plurality of ionimplantation mask layers or the like.

Twentieth Embodiment

Referring to FIG. 93, an example of forming current narrowing layers byperforming heat treatment in a gas phase containing Si thereby diffusingSi atoms in a semiconductor while forming ion-implanted light absorptionlayers by performing ion implantation is described with reference tothis twentieth embodiment. The remaining structure of the twentiethembodiment is similar to that of the first embodiment.

Referring to FIG. 93, an n-type layer 2, an n-type cladding layer 3, anMQW emission layer 4, a p-type cladding layer 5 and a p-type contactlayer 6 are formed on an n-type GaN substrate 1 in this order accordingto this twentieth embodiment, similarly to the first embodiment.

According to the twentieth embodiment, ion-implanted light absorptionlayers 207 a, formed by ion-implanting silicon (Si) excluding a firstwidth of about 1.8 μm, having an implantation depth of about 0.34 μm areprovided on partial regions of the p-type cladding layer 5 and thep-type contact layer 6. Silicon is an example of the “first impurityelementn in the present invention, and the ion-implanted lightabsorption layers 207 a are examples of the “light absorption layer” inthe present invention. In this case, the peak depth of the concentrationof ion-implanted silicon is located in regions of the p-type claddinglayer 5 at a depth of about 0.24 μm from the upper surface of the p-typecontact layer 6. The silicon concentration at this peak depth is about1.0×10²⁰ cm⁻³.

Current narrowing layers 207 b formed by thermally diffusing Si areprovided inside the ion-implanted light absorption layers 207 a. Thesecurrent narrowing layers 207 a perform current narrowing with respect toa current injected from a p side, thereby forming a current passingregion 208 having a width of about 1.5 μm.

A p-side ohmic electrode 209 is formed on the upper surface of thecurrent passing region 208 of the p-type contact layer 6 with anelectrode width of about 2.0 μm in a striped shape, similarly to thefirst embodiment. Insulator films 210 are formed to cover the sidesurfaces of the p-side ohmic electrode 209 and the p-type contact layer6. A p-side pad electrode 211 is formed on the insulator films 210 to bein contact with the upper surface of the p-side ohmic electrode 209. Ann-side ohmic electrode 12 and an n-side pad electrode 13 are formed onthe back surface of the n-type GaN substrate 1 from the side closer tothe back surface of the n-type GaN substrate 1. The thicknesses andcompositions of the respective layers 209 to 211 are similar to those ofthe respective layers 9 to 11 in the first embodiment respectively.

A fabrication process for a nitride semiconductor laser elementaccording to the twentieth embodiment is now described with reference toFIGS. 93 to 97. With reference to this twentieth embodiment, a case offorming the current narrowing layers by thermal diffusion is described.

First, the layers up to the p-type contact layer 6 are formed through aprocess similar to that of the first embodiment shown in FIG. 4. Then,the p-side ohmic electrode 209 consisting of a Pt layer having athickness of about 1 nm, a Pd layer having a thickness of about 50 nm,an Au layer having a thickness of about 240 nm and an Ni layer having athickness of about 240 nm in ascending order is formed on the uppersurface of the p-type contact layer 6 with the electrode width of about2.0 μm in the striped shape by a lift-off method, as shown in FIG. 94.

According to the twentieth embodiment, the p-side ohmic electrode 209 isemployed as a mask for increasing the substrate temperature to about750° C. while holding the element in an SiH₄ gas atmosphere therebythermally diffusing silicon (Si) atoms into the element, as shown inFIG. 95. Thus, the current narrowing layers 207 b increased inresistance are formed. The silicon atoms introduced into the element soisotropically diffuse that the width of the current passing region 208is smaller than that of the p-side ohmic electrode 209 serving as themask. In this case, the width of the current passing region 208 is about1.5 μm. Thus, the current narrowing layers 207 b are so formed bythermal diffusion that the current narrowing layers 207 b can beinhibited from formation of crystal defects.

As shown in FIG. 96, a through film 212 of SiO₂ having a thickness ofabout 60 nm is formed by plasma CVD to cover the overall upper surfacesof the p-side ohmic electrode 209 and the p-type contact layer 6.

According to the twentieth embodiment, the p-side ohmic electrode 209 isemployed as the mask for ion-implanting silicon (Si), thereby formingthe ion-implanted light absorption layers 207 a having the implantationdepth (thickness) of about 0.34 μm from the upper surface of the p-typecontact layer 6. According to the twentieth embodiment, silicon ision-implanted under ion implantation conditions of ion implantationenergy of about 190 keV and a dose of about 2.5×10¹⁵ cm⁻². In this case,the peak depth of the silicon concentration of the ion-implanted lightabsorption layers 207 a is located in the regions of the p-type claddinglayer 5 at the depth of about 0.24 μm from the upper surface of thep-type contact layer 6. The silicon concentration at this peak depth isabout 1.0×10²⁰ cm⁻³. Thereafter the through film 212 is removed with ahydrofluoric acid etchant.

As shown in FIG. 97, the insulator films 210 of SiO₂ having a thicknessof about 200 nm are formed by plasma CVD to cover the overall uppersurfaces of the p-side ohmic electrode 209 and the p-type contact layer6. The upper surface of the p-side ohmic electrode 209 is exposed byphotolithography and RIE with CF₄ gas, similarly to the firstembodiment.

Finally, the p-side pad electrode 211 is formed on the insulator films210 to be in contact with the exposed upper surface of the p-side ohmicelectrode 209 through a process similar to that of the first embodiment.Further, the n-side ohmic electrode 12 and the n-side pad electrode 13are formed on the back surface, polished into a prescribed thickness, ofthe n-type GaN substrate 1 from the side closer to the back surface ofthe n-type GaN substrate 1, thereby completing the nitride semiconductorlaser element according to the twentieth embodiment as shown in FIG. 93.

In the fabrication process for the nitride semiconductor laser elementaccording to the twentieth embodiment, as hereinabove described, thecurrent narrowing layers 207 b increased in resistance are formed bythermally diffusing silicon having reverse conductivity into the p-typecladding layer 5 and the p-type contact layer 6, whereby the number ofcrystal defects in the vicinity of the current passing region 208 can beprevented from increase. Thus, increase of a threshold current can besuppressed.

Twenty-First Embodiment

Referring to FIGS. 98 and 99, an example of forming a ridge portion on ap-type cladding layer while forming ion-implanted light absorptionlayers on regions of this p-type cladding layer other than the ridgeportion is described with reference to this twenty-first embodiment.

First, the structure of a nitride semiconductor laser device accordingto the twenty-first embodiment is described with reference to FIGS. 98and 99. According to the twenty-first embodiment, an n-type layer 302 ofn-type GaN doped with Si having a thickness of about 100 nm and anatomic density of about 5×10¹⁸ cm⁻³ is formed on an n-type GaN substrate301 doped with oxygen having a thickness of about 100 μm and an atomicdensity of about 5×10¹⁸ cm⁻³. An n-type cladding layer 303 of n-typeAl_(0.05)Ga_(0.95)N doped with Si having a thickness of about 400 nm, anatomic density of about 5×10¹⁸ cm⁻³ and a carrier concentration of about5×10¹⁸ cm⁻³ is formed on the n-type layer 302. The n-type layer 302 andthe n-type cladding layer 303 are examples of the “first nitridesemiconductor layer” in the present invention.

An MQW emission layer 304 is formed on the n-type cladding layer 303.This MQW emission layer 304 includes an MQW active layer in which threequantum well layers 304 a of undoped In_(0.15)Ga_(0.85)N each having athickness of about 3 nm and four barrier layers 304 b of undopedIn_(0.05)G_(0.95)N each having a thickness of about 20 nm arealternately stacked, as shown in FIG. 99. An n-type light guide layer304 c of n-type GaN doped with Si having a thickness of about 100 nm, anatomic density of about 5×10¹⁸ cm⁻³ and a carrier concentration of about5×10^(11 cm) ⁻³ and an n-type carrier blocking layer 304 d of n-typeAl_(0.1)Ga_(0.9)N doped with Si having a thickness of about 5 nm, anatomic density of about 5×10¹⁸ cm⁻³ and a carrier concentration of about5×10¹⁸ cm⁻³ are formed on the lower surface of the MQW active layersuccessively from the side closer to the lower surface of the MQW activelayer. Further, a p-type light guide layer 304 e of p-type GaN dopedwith Mg having a thickness of about 100 nm, an atomic density of about4×10¹⁹ cm⁻³ and a carrier concentration of about 5×10¹⁷ cm⁻³ and ap-type cap layer 304 f of p-type Al_(0.1)Ga_(0.9)N doped with Mg havinga thickness of about 20 nm, an atomic density of about 4×10¹⁹ cm⁻³ and acarrier concentration of about 5×10¹⁷ cm⁻³ are successively formed onthe upper surface of the MQW active layer. The MQW emission layer 304 isan example of the “emission layer” in the present invention.

As shown in FIG. 98, a p-type cladding layer 305 of p-typeAl_(0.05)Ga_(0.95)N doped with Mg having a projecting portion with anatomic density of about 4×10¹⁹ cm⁻³ and a carrier concentration of about5×10¹⁷ cm⁻³ is formed on the MQW emission layer 304. The projectingportion of this p-type cladding layer 305 has a width of about 2 μm anda height of about 250 nm. Regions of the p-type cladding layer 305 otherthan the projecting portion have a thickness of about 150 nm. A p-typecontact layer 306 of p-type GaN doped with Mg having a thickness ofabout 10 nm, an atomic density of about 4×10¹⁹ cm⁻³ and a carrierconcentration of about 5×10¹⁷ cm⁻³ is formed on the projecting portionof the p-type cladding layer 305. The projecting portion of the p-typecladding layer 305 and the p-type contact layer 306 constitute a striped(elongated) ridge portion 308 having a width of about 2 μm and a heightof about 260 nm. The p-type cladding layer 305 and the p-type contactlayer 306 are examples of the “second nitride semiconductor layer” inthe present invention.

According to the twenty-first embodiment, ion-implanted light absorptionlayers 307, formed by ion-implanting argon (Ar), having an implantationdepth (thickness) of about 50 nm are provided on the surfaces of flatportions of the p-type cladding layer 305 other than the projectingportion constituting the ridge portion 308. Side ends of theseion-implanted light absorption layers 307 are substantially arrangedimmediately under side ends of the ridge portion 308. Therefore, thewidth (width of optical confinement) W1 between the side ends of theion-implanted light absorption layers 307 is substantially identical tothe width (width of current narrowing) (about 2 μm) of the ridge portion308. Argon is an example of the “first impurity element” in the presentinvention, and the ion-implanted light absorption layers 307 areexamples of the “light absorption layer” in the present invention.

A p-side ohmic electrode 309 consisting of a Pt layer having a thicknessof about 5 nm, a Pd layer having a thickness of about 250 nm and an Aulayer having a thickness of about 250 nm in ascending order is formed onthe p-type contact layer 306 constituting the ridge portion 308.Insulator films 310 of SiN having a thickness of about 250 nm are formedon the surface of the p-type cladding layer 305 and the side surfaces ofthe p-type contact layer 306 and the p-side ohmic electrode 309. Ap-side pad electrode 311 consisting of a Ti layer having a thickness ofabout 100 nm, a Pd layer having a thickness of about 100 nm and an Aulayer having a thickness of about 3 μm in ascending order is formed onthe upper surfaces of the insulator films 310 to be in contact with theupper surface of the p-side ohmic electrode 309. An n-side electrode 312consisting of an Al layer having a thickness of about 10 nm, a Pt layerhaving a thickness of about 20 nm and an Au layer having a thickness ofabout 300 nm successively from the side closer to the back surface ofthe n-type GaN substrate 301 is formed on the back surface of the n-typeGaN substrate 301.

Results obtained by measuring current-light output characteristics andleakage currents of a nitride semiconductor laser element according tothe twenty-first embodiment shown in FIG. 98 and a conventional(comparative) nitride semiconductor laser element in order toinvestigate the difference in performance between these nitridesemiconductor laser elements are now described.

FIG. 100 is a characteristic diagram showing the current-light outputcharacteristics of the nitride semiconductor laser element according tothe twenty-first embodiment shown in FIG. 98 and the conventional(comparative) nitride semiconductor laser element. Referring to FIG.100, the maximum light output is limited to about 9 mW due to outbreakof kinks in the conventional (comparative) nitride semiconductor laserelement. On the other hand, it has been proved that a light output of atleast 9 mW corresponding to the maximum light output of the conventional(comparative) example can be obtained with no kinks in the nitridesemiconductor laser element according to the twenty-first embodiment.This is conceivably because the transverse mode was stabilized due totransverse optical confinement through the ion-implanted lightabsorption layers 307.

Table 1 shows the results obtained by measuring the leakage currents ofthe twenty-first embodiment shown in FIG. 98 and the conventional(comparative) nitride semiconductor laser element. TABLE 1 AppliedVoltage Leakage Current Conventional About 10 V About 1 μA ˜ about 2 μA(Comparative Example) 21st Embodiment At least Not more than about 0.1μA about 10 V

Referring to the above Table 1, a leakage current of about 1 μA to about2 μA was generated in the conventional (comparative) nitridesemiconductor laser element when a voltage of about 10 V was applied. Inthe nitride semiconductor laser element according to the twenty-firstembodiment, on the other hand, only a leakage current of not more thanabout 0.1 μm was generated also when a voltage of at least about 10 Vwas applied.

In the nitride semiconductor laser element according to the twenty-firstembodiment, as hereinabove described, the ion-implanted light absorptionlayers 307 formed by ion implantation are so provided on the surfaceportions of the p-type cladding layer 305 other than the projectingportion constituting the ridge portion 308 that the ion-implanted lightabsorption layers 307 can be formed on the surface portions of thep-type cladding layer 305 other than the projecting portion constitutingthe ridge portion 308 with excellent reproducibility since ionimplantation provides excellent reproducibility. Thus, transverseoptical confinement can be controlled with excellent reproducibility.Consequently, the transverse mode can be stabilized with excellentreproducibility while performing current narrowing through the ridgeportion 308. Further, the transverse mode can be so stabilized thatoutbreak of kinks (bending of the current-light output characteristics)resulting from higher mode oscillation can be suppressed. Thus, a highmaximum light output can be obtained while the beam shape can bestabilized.

The ion-implanted light absorption layers 307 are so provided only onthe surfaces of the flat portions of the p-type cladding layer 305 thata portion having high light intensity in the vicinity of the MQWemission layer 304 can be inhibited from excess light absorption,whereby increase of the threshold current can be suppressed.

A fabrication process for the nitride semiconductor laser elementaccording to the twenty-first embodiment is now described with referenceto FIGS. 98, 99 and 101 to 105.

First, the n-type layer 302, the n-type cladding layer 303, the MQWemission layer 304, the p-type cladding layer 305 and the p-type contactlayer 306 are successively grown on the n-type GaN substrate 301 byatmospheric pressure CVD under a pressure of about 1 atom (about 100kPa), as shown in FIG. 101. The n-type GaN substrate 301 is formed bygrowing GaN on a GaAs substrate by HVPE and thereafter removing the GaAssubstrate having a thickness of not more than 100 μm.

More specifically, the n-type GaN substrate 301 is held at a growthtemperature of about 1100° C. for growing the n-type layer 302 of n-typeGaN doped with Si having the thickness of about 100 nm and the atomicdensity of about 5×10¹⁸ cm⁻³ on the n-type GaN substrate 301 withcarrier gas consisting of H₂ and N₂, source gas consisting of NH₃ andGa(CH₃)₃ and dopant gas consisting of SiH₄. Thereafter Al(CH₃)₃ isfurther added to the source gas for growing the n-type cladding layer303 of n-type Al_(0.05)Ga_(0.95)N doped with Si having the thickness ofabout 400 nm, the atomic density of about 5×10¹⁸ cm⁻³ and the carrierconcentration of about 5×10¹⁸ cm⁻³ on the n-type layer 302.

As shown in FIG. 99, the n-type carrier blocking layer 304 d of n-typeAl_(0.1)Ga_(0.9)N doped with Si having the thickness of about 5 nm, theatomic density of about 5×10¹⁸ cm⁻³ and the carrier concentration ofabout 5×10¹⁸ cm⁻³ is grown on the n-type cladding layer 303 (see FIG.101).

Then, the substrate temperature is held at a growth temperature of 800°C. for growing the n-type light guide layer 304 c of n-type GaN dopedwith Si having the atomic density of about 5×10¹⁸ cm⁻³ and the carrierconcentration of about 5×10¹⁸ cm⁻³ on the n-type carrier blocking layer304 d with carrier gas consisting of H₂ and N₂, source gas consisting ofNH₃ and Ga(CH₃)₃ and dopant gas consisting of SiH₄.

Thereafter In(CH₃)₃ is further added to the source gas for alternatelygrowing the three quantum well layers 304 a of undopedIn_(0.15)Ga_(0.85)N each having the thickness of about 3 nm and the fourbarrier layers 304 b of undoped In_(0.05)G_(0.95)N each having thethickness of about 20 nm on the n-type light guide layer 304 c withoutemploying dopant gas thereby forming the MQW active layer.

The source gas is changed to NH₃ and Ga(CH₃)₃ while employing dopant gasconsisting of CP₂Mg for growing the p-type light guide layer 304 e ofp-type GaN doped with Mg having the thickness of about 100 nm, theatomic density of about 4×10¹⁹ cm⁻³ and the carrier concentration ofabout 5×10¹⁷ cm⁻³ on the MQW active layer. Thereafter Al(CH₃)₃ isfurther added to the source gas for growing the p-type cap layer 304 fof p-type Al_(0.1)Ga_(0.9)N doped with Mg having the thickness of about20 nm, the atomic density of about 4×10¹⁹ cm⁻³ and the carrierconcentration of about 5×10¹⁷ cm⁻³ on the p-type light guide layer 304e. Thus, the MQW emission layer 304 consisting of the quantum welllayers 304 a, the barrier layers 304 b, the n-type light guide layer 304c, the n-type carrier blocking layer 304 d, the p-type light guide layer304 e and the p-type cap layer 304 f is formed.

As shown in FIG. 101, the substrate temperature is held at a growthtemperature of 1100° C. for growing the p-type cladding layer 305 ofp-type Al_(0.05)Ga_(0.95)N doped with Mg having the thickness of about400 nm, the atomic density of about 4×10¹⁹ cm⁻³ and the carrierconcentration of about 5×10¹⁷ cm⁻³ on the MQW emission layer 304 withcarrier gas consisting of H₂ and N₂, source gas consisting of NH₃,Ga(CH₃)₃ and Al(CH₃)₃ and dopant gas consisting of CP₂Mg. Thereafter thesource gas is changed to NH₃ and Ga(CH₃)₃ for growing the p-type contactlayer 306 of p-type GaN doped with Mg having the thickness of about 10nm, the atomic density of about 4×10¹⁹ cm⁻³ and the carrierconcentration of about 5×10¹⁷ cm⁻³ on the p-type cladding layer 305.

Thereafter annealing is performed in a nitrogen gas atmosphere under atemperature condition of about 800° C.

As shown in FIG. 102, the p-side ohmic electrode 309 consisting of thePt layer having the thickness of about 5 nm, the Pd layer having thethickness of about 250 nm and the Au layer having the thickness of about250 nm in ascending order and an Ni layer 313 having a thickness ofabout 250 nm are successively formed on the p-type contact layer 306,and the p-side ohmic electrode 309 and the Ni layer 313 are thereafterpatterned into striped (elongated) shapes having a width of about 2 μm.

As shown in FIG. 103, the Ni layer 313 is employed as a mask fordry-etching portions of the p-type contact layer 306 and the p-typecladding layer 305 having a thickness of about 250 nm from the uppersurfaces with Cl₂ gas. Thus, the striped (elongated) ridge portion 308,constituted of the projecting portion of the p-type cladding layer 305and the p-type contact layer 306, having the width of about 2 μm and theheight of about 260 nm is formed. Thereafter the Ni layer 313 isremoved.

According to the twenty-first embodiment, the p-side ohmic electrode 309is employed as a mask for ion-implanting argon (Ar) into the flatportions of the p-type cladding layer 305 other than the projectingportion constituting the ridge portion 308 thereby forming theion-implanted light absorption layers 307 having the ion implantationdepth (thickness) of about 50 nm, as shown in FIG. 104. At this time,the p-side ohmic electrode 309 having the width (about 2 μm)substantially identical to that of the ridge portion 308 is so employedas the mask that the side ends of the ion-implanted light absorptionlayers 307 are substantially arranged immediately under the side ends ofthe ridge portion 308 while the width (width of optical confinement) WIbetween the side ends of the ion-implanted light absorption layers 307is about 2 μm. Ion implantation conditions for argon are implantationenergy of about 40 keV, a dose of about 1×10¹² cm⁻² to about 1×10¹³ cm⁻²and an implantation temperature of the room temperature. Ionimplantation is performed from a direction inclined by about 70 in thelongitudinal direction of the p-side ohmic electrode 309.

As shown in FIG. 105, the insulator films 310 of SiN having thethickness of about 250 nm are thereafter formed to cover the overallsurface and a portion of the insulator films 310 located on the uppersurface of the p-side ohmic electrode 309 is removed. Thus, the uppersurface of the p-side ohmic electrode 309 is exposed.

Finally, the p-side pad electrode 311 consisting of the Ti layer havingthe thickness of about 100 nm, the Pd layer having the thickness ofabout 100 nm and the Au layer having the thickness of about 3 μm inascending order is formed on the upper surfaces of the insulator films310 by vacuum evaporation to be in contact with the upper surface of thep-side ohmic electrode 309, as shown in FIG. 98. Further, the n-sideelectrode 312 consisting of the Al layer having the thickness of about10 nm, the Pt layer having the thickness of about 20 nm and the Au layerhaving the thickness of about 300 nm successively from the side closerto the back surface of the n-type GaN substrate 301 is formed on theback surface of the n-type GaN substrate 301 by vacuum evaporation.Thus, the nitride semiconductor laser element according to thetwenty-first embodiment is completed.

In the fabrication process for the nitride semiconductor laser elementaccording to the twenty-first embodiment, as hereinabove described, theridge portion 308 is formed before forming the ion-implanted lightabsorption layers 307 by ion-implanting argon (Ar) so that theimplantation depth may not be increased, whereby the implantation energycan be reduced to about 40 keV. Thus, the spreading width of theimpurity profile can be so reduced that the implantation depth can beprecisely controlled. Consequently, the impurity element (argon) can beprevented from reaching the MQW emission layer 304, whereby the MQWemission layer 304 can be prevented from damage by the impurity element(argon).

Twenty-Second Embodiment

Referring to FIG. 106, an example of increasing the width between sideends of ion-implanted light absorption layers (width of opticalconfinement) beyond the width of a ridge portion (width of currentnarrowing) while setting an ion implantation depth to a level reachingan n-type cladding layer dissimilarly to the twenty-first embodiment isdescribed with reference to this twenty-second embodiment. The remainingstructure of the twenty-second embodiment is similar to that of thetwenty-first embodiment.

Referring to FIG. 106, an n-type layer 302, an n-type cladding layer303, an MQW emission layer 304, a p-type cladding layer 305 and a p-typecontact layer 306 are successively formed on an n-type GaN substrate 301according to this twenty-second embodiment, similarly to thetwenty-first embodiment. A projecting portion of the p-type claddinglayer 305 and the p-type contact layer 306 constitute a striped(elongated) ridge portion 308 having a width of about 2 μm and a heightof about 260 nm.

According to the twenty-second embodiment, ion-implanted lightabsorption layers 327, formed by ion-implanting carbon (C), having animplantation depth (thickness) of about 300 nm are provided. Theseion-implanted light absorption layers 327 are formed over the surfacesof flat portions of the p-type cladding layer 305 other than theprojecting portion constituting the ridge portion 308 to the MQWemission layer 304 and the n-type cladding layer 303. Further, the sideends of the ion-implanted light absorption layers 327 are arranged onpositions transversely separated from the side ends of the ridge portion308 by the thickness (not more than about 2 μm) of insulator films 330described later. Therefore, the width W2 (width of optical confinement)between the side ends of the ion-implanted light absorption layers 327has a size (not more than about 6 μm) larger than the width (width ofcurrent narrowing) (about 2 μm) of the ridge portion 308. Further, thepeak depth of the impurity concentration of the ion-implanted lightabsorption layers 327 is located in portions of the p-type claddinglayer 305 at about 130 nm from the surfaces of the flat portions of thep-type cladding layer 305 other than the projecting portion constitutingthe ridge portion 308. The ion-implanted light absorption layers 327 areexamples of the “light absorption layer” in the present invention.

A p-side ohmic electrode 309 is formed on the p-type contact layer 306constituting the ridge portion 308. The insulator films 330 of SiO₂ alsohaving a function as masks for ion implantation are formed on thesurface of the p-type cladding layer 305 and the side surfaces of thep-type contact layer 306 and the p-side ohmic electrode 309. Thethickness of these insulator films 330 is not more than about 2 μm,substantially identically to the width W3 between the side ends of theridge portion 308 and the side ends of the ion-implanted lightabsorption layers 327. A p-side pad electrode 331 having a thickness anda composition similar to those in the twenty-first embodiment is formedon the upper surfaces of the insulator films 330 to be in contact withthe upper surface of the p-side ohmic electrode 309. An n-side electrode312 is formed on the back surface of the n-type GaN substrate 301.

Results obtained by measuring aspect ratios of beams in order toinvestigate difference between beam shapes according near field patternsof an ion-implanted nitride semiconductor laser element according to thetwenty-second embodiment shown in FIG. 106 and a conventional(comparative) non-ion-implanted nitride semiconductor laser element arenow described. Table 2 shows the results of this measurement. TABLE 2Dose: about Dose: about 1 × 10¹³ cm⁻² 1 × 10¹⁴ cm⁻² Non- Implanted Ions:Implanted Ions: Implanted Carbon (C) Carbon (C) Aspect Ratio 4:1 2:1 1:1(transverse: longitudinal)

Referring to the above Table 2, the aspect ratio(transverse:longitudinal) of the beam was 4:1 in the conventional(comparative) non-ion-implanted nitride semiconductor laser element. Inthe ion-implanted nitride semiconductor laser element according to thetwenty-second embodiment, on the other hand, the aspect ratio(transverse:longitudinal) of the beam was 2:1 when the dose was about1×10¹³ cm⁻². Further, the aspect ratio (transverse:longitudinal) of thebeam was 1:1 when the dose was about 1×10¹⁴ cm⁻². This is conceivablybecause transverse spreading of light was suppressed due to transverseoptical confinement through the ion-implanted light absorption layers327. Further, light absorption is increased as the dose is increased,and hence the aspect ratio is conceivably improved so that the beamapproaches a true circle.

In the nitride semiconductor laser element according to thetwenty-second embodiment, as hereinabove described, the width W2 (widthof optical confinement) between the side ends of the ion-implanted lightabsorption layers 327 is rendered larger than the width (about 2 μm) ofthe ridge portion 308 so that the portion having high light intensity inthe vicinity of the MQW emission layer 304 can be inhibited from excesslight absorption while current narrowing can be strengthened. Thus,transverse optical confinement of the MQW emission layer 304 can beexcellently performed while further suppressing increase of thethreshold current. Consequently, the transverse mode can be so furtherstabilized that the beam shape can be further stabilized. Further,outbreak of kinks (bending of current-light output characteristics)resulting from higher mode oscillation can be so further suppressed thata higher maximum light output can be obtained.

According to the twenty-second embodiment, further, the ion-implantedlight absorption layers 327 formed by ion implantation are so providedon the regions of the p-type cladding layer 305 other than theprojecting portion constituting the ridge portion 308 that theion-implanted light absorption layers 327 can be formed with excellentreproducibility, whereby transverse optical confinement can becontrolled with excellent reproducibility. Consequently, the transversemode can be stabilized with excellent reproducibility while performingcurrent narrowing through the ridge portion 308.

A fabrication process for the nitride semiconductor laser elementaccording to the twenty-second embodiment is now described withreference to FIGS. 106 to 109.

First, the layers up to the striped (elongated) ridge portion 308,constituted of the projecting portion of the p-type cladding layer 305and the p-type contact layer 306, having the width of about 2 μm and theheight of about 260 nm are formed as shown in FIG. 107 through afabrication process similar to that of the twenty-first embodiment shownin FIGS. 101 to 103. Thereafter the insulator film 330 of SiO₂ havingthe thickness of not more than about 2 μm is formed to cover the overallsurface.

According to the twenty-second embodiment, the insulator film 330 isemployed as a mask for ion-implanting carbon (C), as shown in FIG. 108.Thus, the ion-implanted light absorption layers 327 having the ionimplantation depth (thickness) of about 300 nm are formed over thesurfaces of the flat portions of the p-type cladding layer 305 otherthan the projecting portion constituting the ridge portion 308 to theMQW emission layer 304 and the n-type cladding layer 303. At this time,not only the portion of the insulator film 330 located on the uppersurface of the ohmic electrode 309 but also the portions located on theside ends of the ridge portion 308 form the mask, whereby the side endsof the ion-implanted light absorption layers 327 are formed on thepositions transversely separated from the side ends of the ridge portion308 by the thickness (not more than about 2 μm) of the insulator film330. Therefore, the width (width of optical confinement) W2 between theside ends of the ion-implanted light absorption layers 327 exceeds thewidth (width of current narrowing) (about 2 μm) of the ridge portion 308while the width W3 between the side ends of the ridge portion 308 andthe side ends of the ion-implanted light absorption layers 327 is notmore than about 2 μm. Further, the peak depth of the impurityconcentration of the ion-implanted light absorption layers 327 islocated in the portions of the p-type cladding layer 305 at about 130 nmfrom the surfaces of the flat portions of the p-type cladding layer 305other than the projecting portion constituting the ridge portion 308.Ion implantation conditions for carbon are implantation energy of about95 keV, a dose of about 1×10¹³ cm⁻² to about 1×10¹⁴ cm⁻² and animplantation temperature of the room temperature. This ion implantationis performed from a direction inclined by about 70 in the longitudinaldirection of the p-side ohmic electrode 309.

Thereafter the portion of the insulator film 330 located on the uppersurface of the p-side ohmic electrode 309 is removed, as shown in FIG.109. Thus, the upper surface of the p-side ohmic electrode 309 isexposed.

Finally, the p-side pad electrode 331 having the thickness and thecomposition similar to those in the twenty-first embodiment is formed onthe upper surfaces of the insulator films 330 to be in contact with theupper surface of the p-side ohmic electrode 309, as shown in FIG. 106.Further, the n-side electrode 312 is formed on the back surface of then-type GaN substrate 301. Thus, the nitride semiconductor laser elementaccording to the twenty-second embodiment is completed.

Twenty-Third Embodiment

Referring to FIG. 110, an example of forming a ridge portion after ionimplantation dissimilarly to the aforementioned twenty-first andtwenty-second embodiments is described with reference to thistwenty-third *embodiment. The remaining structure of the twenty-thirdembodiment is similar to that of the twenty-first embodiment.

Referring to FIG. 110, an n-type layer 302, an n-type cladding layer 303and an MQW emission layer 304 are successively formed on an n-type GaNsubstrate 301 according to this twenty-third embodiment, similarly tothe twenty-first embodiment.

According to the twenty-third embodiment, a p-type cladding layer 345 ofp-type Al_(0.05)Ga_(0.95)N doped with Mg having a projecting portion isformed on the MQW emission layer 304. The projecting portion of thisp-type cladding layer 345 has a width of about 2 μm and a height ofabout 260 nm. Further, flat portions of the p-type cladding layer 345other than the projecting portion have a thickness of about 140 nm. Ap-type contact layer 306 is formed on the projecting portion of thep-type cladding layer 345. The projecting portion of the p-type claddinglayer 345 and the p-type contact layer 306 constitute a striped(elongated) ridge portion 348 having a width of about 2 μm and a heightof about 270 nm. The p-type cladding layer 345 is an example of the“second nitride semiconductor layer” in the present invention.

According to the twenty-third embodiment, ion-implanted light absorptionlayers 347, formed by ion-implanting carbon (C), having an implantationdepth (thickness) of about 240 nm are provided. These ion-implantedlight absorption layers 347 are formed over the surfaces of the flatportions of the p-type cladding layer 345 other than the projectingportion constituting the ridge portion 348 to the MQW emission layer 304and the n-type cladding layer 303. Further, the side ends of theion-implanted light absorption layers 347 are arranged on positionstransversely separated from the side ends of the ridge portion 348 bythe thickness (not more than about 2 μm) of an ion implantation mask 354described later. Therefore, the width (width of optical confinement) W4between the side ends of the ion-implanted light absorption layers 347has a size (not more than about 6 μm) larger than the width (width ofcurrent narrowing) (about 2 μm) of the ridge portion 348. The peak depthof the impurity concentration of the ion-implanted light absorptionlayers 347 is located on the surfaces of the flat portions of the p-typecladding layer 345 other than the projecting portion constituting theridge portion 348. The ion-implanted light absorption layers 347 areexamples of the “light absorption layer” in the present invention.

A p-side ohmic electrode 309 is formed on the p-type contact layer 306constituting the ridge portion 348. Insulator films 310 are formed onthe surface of the p-type cladding layer 345 and the side surfaces ofthe p-type contact layer 306 and the p-side ohmic electrode 309. Ap-side pad electrode 311 is formed on the upper surfaces of theinsulator films 310 to be in contact with the upper surface of thep-side ohmic electrode 309. An n-side electrode 312 is formed on theback surface of the n-type GaN substrate 301.

In a nitride semiconductor laser element according to the twenty-thirdembodiment, as hereinabove described, the peak depth of the impurityconcentration of the ion-implanted light absorption layers 347 islocated on the surfaces of the flat portions of the p-type claddinglayer 345 other than the projecting portion constituting the ridgeportion 348 so that a portion having high light intensity in thevicinity of the MQW emission layer 304 can be inhibited from excesslight absorption, whereby increase of the threshold current can besuppressed.

The remaining effects of the twenty-third embodiment are similar tothose of the twenty-second embodiment.

A fabrication process for the nitride semiconductor laser elementaccording to the twenty-third embodiment is now described with referenceto FIGS. 110 to 114.

First, the n-type layer 302, the n-type cladding layer 303 and the MQWemission layer 304 are successively formed on the n-type GaN substrate301 through a fabrication process similar to that of the firstembodiment, as shown in FIG. 111. Then, the p-type cladding layer 345 ofp-type Al_(0.05)Ga_(0.95)N having a thickness of about 400 nm and thep-type contact layer 306 are successively formed on the MQW emissionlayer 304. Thereafter annealing is performed in a nitrogen gasatmosphere under a temperature condition of about 800° C. Then, thep-side ohmic electrode 309 and an Ni layer 313 are successively formedon the p-type contact layer 306, and the p-side ohmic electrode 309 andthe Ni layer 313 are thereafter patterned into striped (elongated)shapes having a width of about 2 μm. Then, the ion implantation mask 354of SiO₂ having the thickness of not more than about 2 μm is formed tocover the overall surface.

According to the twenty-third embodiment, the ion implantation mask 354is employed as a mask for ion-implanting carbon (C), as shown in FIG.112. Thus, the ion-implanted light absorption layers 347 having an ionimplantation depth (thickness) of about 510 nm are formed over the uppersurface portion of the p-type contact layer 306 other than the regionformed with the p-side ohmic electrode 309 to the MQW emission layer 304and the n-type cladding layer 303. At this time, not only the portion ofthe ion implantation mask 354 located on the upper surface of the Nilayer 313 but also portions located on the side ends of the p-side ohmicelectrode 309 and the Ni layer 313 form the mask, whereby the side endsof the ion-implanted light absorption layers 347 are formed on positionstransversely separated from the side ends of the p-side ohmic electrode309 and the Ni layer 313 by the thickness (not more than about 2 μm) ofthe ion implantation mask 354. Therefore, the width (width of opticalconfinement) W4 between the side ends of the ion-implanted lightabsorption layers 347 exceeds the width (about 2 μm) of the p-side ohmicelectrode 309 and the Ni layer 313. Further, the peak depth of theimpurity concentration of the ion-implanted light absorption layers 347is located in portions of the p-type cladding layer 345 at about 270 nmfrom the upper surface of the p-type contact layer 306 other than theregion formed with the p-side ohmic electrode 309. Ion implantationconditions for carbon are implantation energy of about 190 keV, a doseof about 1×10¹³ cm⁻² to about 1×10¹⁴ cm⁻² and an implantationtemperature of the room temperature. This ion implantation is performedfrom a direction inclined by about 70 in the longitudinal direction ofthe p-side ohmic electrode 309. Thereafter the ion implantation mask 354is removed.

As shown in FIG. 113, the Ni layer 313 is employed as a mask forpartially dry-etching the p-type contact layer 306 and the p-typecladding layer 345 by a thickness of about 260 nm from the uppersurfaces with Cl₂ gas. Thus, the striped (elongated) ridge portion 348,constituted of the projecting portion of the p-type cladding layer 345and the p-type contact layer 306, having the width of about 2 μm and theheight of about 270 nm is formed. According to this etching, the peakdepth of the impurity concentration of the ion-implanted lightabsorption layers 347 having Gaussian distribution is located on thesurfaces of the flat portions of the p-type cladding layer 345 otherthan the projecting portion constituting the ridge portion 348. Further,the width (width of optical confinement) W4 between the side ends of theion-implanted light absorption layers 347 has the size (not more thanabout 6 μm) larger than the width (width of current narrowing) (about 2μm) of the ridge portion 348, while the width W5 between the side endsof the ridge portion 348 and the side ends of the ion-implanted lightabsorption layers 347 is substantially identical to the thickness (notmore than about 2 μm) of the ion implantation mask 354 (see FIG. 112).Thereafter the Ni layer 313 is removed.

Then, the insulator films 310 are formed to cover the overall surfaceand the portion of the insulator films 310 located on the upper surfaceof the p-side ohmic electrode 309 is thereafter removed, as shown inFIG. 114. Thus, the upper surface of the p-side ohmic electrode 309 isexposed.

Finally, the p-side pad electrode 311 is formed on the upper surfaces ofthe insulator films 310 to be in contact with the upper surface of thep-side ohmic electrode 309, as shown in FIG. 110. Further, the n-sideelectrode 312 is formed on the back surface of the n-type GaN substrate301. Thus, the nitride semiconductor laser element according to thetwenty-third embodiment is completed.

In the fabrication process for the nitride semiconductor laser elementaccording to the twenty-third embodiment, as hereinabove described, theridge portion 348 is formed by forming the ion-implanted lightabsorption layers 347 over the upper surface of the p-type contact layer306 to the MOW emission layer 304 and the n-type cladding layer 303 andthereafter performing etching up to the peak depth of the impurityconcentration of the ion-implanted light absorption layers 347, wherebythe depth of the impurity concentration of the ion-implanted lightabsorption layers 347 having the Gaussian distribution can be easilylocated on the surface portions of the p-type cladding layer 347.Further, the spreading width of the impurity profile is increased due tothe high implantation energy of about 190 keV. Thus, the profile in thevicinity of the peak depth of the impurity (carbon) concentration can beflattened, whereby the light absorption function of the ion-implantedlight absorption layers 347 can be flattened (uniformized).Consequently, transverse optical confinement can be stabilized.

Twenty-Fourth Embodiment

Referring to FIG. 115, an example of forming ion-implanted lightabsorption layers on both side portions of a ridge portion and flatportions of a p-type cladding layer other than a projecting portionconstituting the ridge portion dissimilarly to the aforementionedtwenty-first to twenty-third embodiment is described with reference tothis twenty-fourth embodiment. The remaining structure of thetwenty-fourth embodiment is similar to that of the twenty-firstembodiment.

Referring to FIG. 115, an n-type layer 302, an n-type cladding layer 303and an MQW emission layer 304 are successively formed on an n-type GaNsubstrate 301 in this twenty-fourth embodiment, similarly to thetwenty-first embodiment.

A p-type cladding layer 365 of p-type Al_(0.05)Ga_(0.95)N doped with Mghaving a projecting portion is formed on the MQW emission layer 304. Theprojecting portion of this p-type cladding layer 365 has a width ofabout 2 μm and a height of about 300 nm. Further, flat portions of thep-type cladding layer 365 other than the projecting portion are formedin a striped (elongated) shape having a thickness of about 100 nm. Ap-type contact layer 306 is formed on the projecting portion of thep-type cladding layer 365. The projecting portion of the p-type claddinglayer 365 and the p-type contact layer 306 constitute a striped(elongated) ridge portion 368 having a width of about 2 μm and a heightof about 310 nm. The p-type cladding layer 365 is an example of the“second nitride semiconductor layer” in the present invention.

According to the twenty-fourth embodiment, ion-implanted lightabsorption layers 367, formed by ion-implanting carbon (C), havinglongitudinal and transverse implantation depths (thicknesses) of about200 nm are provided on both side surfaces of the ridge portion 368 andthe flat portions of the p-type cladding layer 365 other than theprojecting portion. Therefore, the width (width of optical confinement)W6 between side ends of the ion-implanted light absorption layers 367has a size (about 1.6 μm) smaller than the width (about 2 μm) of theridge portion 368. The ion-implanted light absorption layers 367 areexamples of the “light absorption layer” in the present invention.

A p-side ohmic electrode 309 is formed on the p-type contact layer 306constituting the ridge portion 368. Channeling prevention films 370 a ofSiN having a thickness of about 40 nm are formed on the surface of thep-type cladding layer 365 and the side surfaces of the p-type contactlayer 306 and the p-side ohmic electrode 309. These channelingprevention films 370 a have a function of suppressing channeling in anion implantation process. Insulator films 370 b of SiN having athickness of about 210 nm are formed on the surfaces of the channelingprevention films 370 a. A p-side pad electrode 311 is formed on theupper surfaces of the insulator films 370 b to be in contact with theupper surface of the p-side ohmic electrode 309. An n-side electrode 312is formed on the back surface of the n-type GaN substrate 301.

In a nitride semiconductor laser element according to the twenty-fourthembodiment, as hereinabove described, the ion-implanted light absorptionlayers 367 are provided on both side surfaces of the ridge portion 368and the flat portions of the p-type cladding layer 365 other than theprojecting portion so that transverse optical confinement can beexcellently performed through both side surfaces of the ridge portion368 and the flat portions of the ridge portion 368 of the p-typecladding layer 365.

The remaining effects of the twenty-fourth embodiment are similar tothose of the twenty-first embodiment.

A fabrication process for the nitride semiconductor laser elementaccording to the twenty-fourth embodiment is now described withreference to FIGS. 115 to 118.

As shown in FIG. 116, the n-type layer 302, the n-type cladding layer303 and the MQW emission layer 304 are successively formed on the n-typeGaN substrate 301 through a fabrication process similar to that of thetwenty-first embodiment. The p-type cladding layer 365 of p-typeAl_(0.05)Ga_(0.95)N doped with Mg having a thickness of about 400 nm andthe p-type contact layer 306 are successively formed on the MQW emissionlayer 304. Thereafter annealing is performed in a nitrogen gasatmosphere under a temperature condition of about 800° C. Then, thep-side ohmic electrode 309 and an Ni layer (not shown) are successivelyformed on the p-type contact layer 306, and the p-side ohmic electrode309 and the Ni layer are thereafter patterned into striped (elongated)shapes having a width of about 2 μm. Then, the Ni layer is employed as amask for partially etching the p-type contact layer 306 and the p-typecladding layer 365 by a thickness of about 300 nm from the uppersurfaces. Thus, the striped (elongated) ridge portion 368, constitutedof the projecting portion of the p-type cladding layer 365 and thep-type contact layer 306, having the width of about 2 μm and the heightof about 310 nm is formed. Then, the Ni layer is removed and thechanneling prevention films 370 a of SiN having the thickness of about40 nm are thereafter formed to cover the overall surface.

According to the twenty-fourth embodiment, the p-side ohmic electrode309 is employed as a mask for ion-implanting carbon (C) through thechanneling prevention films 370 a, as shown in FIG. 117. At this time,ion implantation is performed from an oblique direction of 45° once eachtime so that ions are implanted into both side portions of the ridgeportion 368. Thus, the ion-implanted light absorption layers 367 havingthe longitudinal and transverse implantation depths (thicknesses) ofabout 200 nm are formed on both side surfaces of the ridge portion 368and the flat portions of the p-type cladding layer 365 other than theprojecting portion. Further, the width (width of optical confinement) W6between the side ends of the ion-implanted light absorption layers 367is about 1.6 μm. In addition, ion-implanted regions are so increased inresistance that the current narrowing width also reaches the width W6.Ion implantation conditions for carbon are implantation energy of about95 keV, a dose of about 1×10¹³ cm⁻² to about 1×10¹⁴ cm⁻² and animplantation temperature of the room temperature.

Thereafter the insulator films 370 b of SiN having the thickness ofabout 210 nm are formed to cover the overall surface and portions of thechanneling prevention layers 370 a and the insulator films 370 b locatedon the upper surface of the p-side ohmic electrode 309 are removed, asshown in FIG. 118. Thus, the upper surface of the p-side ohmic electrode309 is exposed.

Finally, the p-side pad electrode 311 is formed on the upper surfaces ofthe insulator films 370 b to be in contact with the upper surface of thep-side ohmic electrode 309. Further, the n-side electrode 312 is formedon the back surface of the n-type GaN substrate 301. Thus, the nitridesemiconductor laser element according to the twenty-fourth embodiment iscompleted.

In the fabrication process for the nitride semiconductor laser elementaccording to the twenty-fourth embodiment, as hereinabove described, theridge portion 368 is formed before forming the ion-implanted lightabsorption layers 367 by ion-implanting carbon (C) so that theimplantation depth may not be increased, whereby the implantation energycan be reduced to about 95 keV. Thus, the impurity element (carbon) canbe prevented from reaching the MQW emission layer 304 similarly to thetwenty-first embodiment, whereby the MQW emission layer 304 can beprevented from damage by the impurity element (carbon).

Twenty-Fifth Embodiment

Referring to FIG. 119, an example of forming ion-implanted lightabsorption layers only on both side surfaces of a ridge portiondissimilarly to the aforementioned twenty-first to twenty-fourthembodiments is described with reference to this twenty-fifth embodiment.The remaining structure of the twenty-fifth embodiment is similar tothat of the twenty-first embodiment.

Referring to FIG. 119, an n-type layer 302, an n-type cladding layer 303and an MQW emission layer 304 are successively formed on an n-type GaNsubstrate 301 according to this twenty-fifth embodiment, similarly tothe twenty-first embodiment.

According to the twenty-fifth embodiment, a p-type cladding layer 385 ofp-type Al_(0.05)Ga_(0.95)N doped with Mg having a projecting portion isformed on the MQW emission layer 304. The projecting portion of thisp-type cladding layer 385 is formed in a striped (elongated) shapehaving a width of about 2 μm and a height of about 300 nm. Further, flatportions of the p-type cladding layer 385 other than the projectingportion have a thickness of about 100 nm. A p-type contact layer 306 isformed on the projecting portion of the p-type cladding layer 385. Theprojecting portion of the p-type cladding layer 385 and the p-typecontact layer 306 constitute a striped (elongated) ridge portion 388having a width of about 2 μm and a height of about 310 nm. The p-typecladding layer 385 is an example of the “second nitride semiconductorlayer” in the present invention.

According to the twenty-fifth embodiment, ion-implanted light absorptionlayers 387, formed by ion-implanting carbon (C), having a transverseimplantation depth (thickness) of about 200 nm are provided on both sidesurfaces of the ridge portion 388. Therefore, the width (width ofoptical confinement) W7 between side ends of the ion-implanted lightabsorption layers 387 has a size (about 1.6 μm) smaller than the width(about 2 μm) of the ridge portion 388. The ion-implanted lightabsorption layers 387 are examples of the “light absorption layer” inthe present invention.

A p-side ohmic electrode 309 is formed on the p-type contact layer 306constituting the ridge portion 388. Insulator films 310 are formed onthe surface of the p-type cladding layer 385 and the side surfaces ofthe p-type contact layer 306 and the p-side ohmic electrode 309. Ap-side pad electrode 311 is formed on the upper surfaces of theinsulator films 310 to be in contact with the upper surface of thep-side ohmic electrode 309. An n-side electrode 312 is formed on theback surface of the n-type GaN substrate 301.

In a nitride semiconductor laser element according to the twenty-fifthembodiment, as hereinabove described, the ion-implanted light absorptionlayers 387 are so provided on both side surfaces of the ridge portion388 that transverse optical confinement can be performed in the ridgeportion 388.

The remaining effects of the twenty-fifth embodiment are similar tothose of the twenty-first embodiment.

A fabrication process for the nitride semiconductor laser elementaccording to the twenty-fifth embodiment is now described with referenceto FIGS. 119 to 123.

As shown in FIG. 120, the n-type layer 302, the n-type cladding layer303 and the MQW emission layer 304 are successively formed on the n-typeGaN substrate 301 through a fabrication process similar to that of thetwenty-first embodiment. Then, the p-type cladding layer 385 of p-typeAl_(0.05)Ga_(0.95)N having a thickness of about 400 nm and the p-typecontact layer 306 are successively formed on the MQW emission layer 304.Thereafter annealing is performed in a nitrogen gas atmosphere under atemperature condition of about 800° C. Then, the p-side ohmic electrode309 and an Ni layer 313 are successively formed on the p-type contactlayer 306, and the p-side ohmic electrode 309 and the Ni layer 313 arethereafter patterned into striped (elongated) shapes having a width ofabout 2 μm. Then, the Ni layer 313 is employed as a mask for partiallyetching the p-type contact layer 306 and the p-type cladding layer 385by a thickness of about 150 nm from the upper surfaces. Thereafter achanneling prevention film 394 of SiN having a thickness of about 40 nmis formed to cover the overall surface.

According to the twenty-fifth embodiment, the p-side ohmic electrode 309and the Ni layer 313 are employed as masks for ion-implanting carbon, asshown in FIG. 121. At this time, ion implantation is performed from anoblique direction of 45° once each time so that ions are implanted intoboth sides of the projecting portion of the p-type cladding layer 385and the p-type contact layer 306. Thus, the ion-implanted lightabsorption layers 387 having longitudinal and transverse implantationdepths (thicknesses) of about 200 nm are formed on both side surfaces ofthe projecting portion of the p-type cladding layer 385 and the p-typecontact layer 306 and the flat portions of the p-type cladding layer 385other than the projecting portion. Further, the width (width of opticalconfinement) W7 between the side ends of the ion-implanted lightabsorption layers 387 is about 1.6 μm. In addition, ion-implantedregions are so increased in resistance that the current narrowing widthalso reaches the width W7. Ion implantation conditions for carbon areimplantation energy of about 95 keV, a dose of about 1×10¹³ cm⁻² toabout 1×10¹⁴ cm⁻² and an implantation temperature of the roomtemperature. Thereafter the channeling prevention film 394 is removed.

According to the twenty-fifth embodiment, the Ni layer 313 is employedas a mask for dry-etching the regions of the p-type cladding layer 385formed with the ion-implanted light absorption layers 387 by a thicknessof about 150 nm from the surface with Cl₂ gas, as shown in FIG. 122.Thus, portions of the ion-implanted light absorption layers 387 formedon the flat portions of the p-type cladding layer 385 are removed.Consequently, the ion-implanted light absorption layers 385 are arrangedonly on both side surfaces of the ridge portion 388. Further, thestriped (elongated) ridge portion 388, constituted of the projectingportion of the p-type cladding layer 385 and the p-type contact layer306, having the width of about 2 μm and the height of about 310 nm isformed by this etching. Thereafter the Ni layer 313 is removed.

Thereafter the insulator films 310 are formed to cover the overallsurface and a portion of the insulator films 310 located on the uppersurface of the p-side ohmic electrode 309 is removed, as shown in FIG.123. Thus, the upper surface of the p-side ohmic electrode 309 isexposed.

Finally, the p-side pad electrode 311 is formed on the upper surfaces ofthe insulator films 310 to be in contact with the upper surface of thep-side ohmic electrode 309, as shown in FIG. 119. Further, the n-sideelectrode 312 is formed on the back surface of the n-type GaN substrate301. Thus, the nitride semiconductor laser element according to thetwenty-fifth embodiment is completed.

Twenty-Sixth Embodiment

Referring to FIG. 124, an example of providing ion-implanted lightabsorption layers dividedly on side ends of a ridge portion and sideends of an element dissimilarly to the aforementioned twenty-first totwenty-fifth embodiments is described with reference to thistwenty-sixth embodiment.

Referring to FIG. 124, an n-type layer 302, an n-type cladding layer303, an MQW emission layer 304, a p-type cladding layer 305 and a p-typecontact layer 306 are successively formed on an n-type GaN substrate 301according to this twenty-sixth embodiment, similarly to the twenty-firstembodiment. A projecting portion of the p-type cladding layer 305 andthe p-type contact layer 306 constitute a striped (elongated) ridgeportion 308 having a width of about 2 μm and a height of about 260 nm.

According to the twenty-sixth embodiment, ion-implanted light absorptionlayers 407, formed by ion-implanting carbon (C), having an implantationdepth (thickness) of about 300 nm are provided. These ion-implantedlight absorption layers 407 are divided into ion-implanted lightabsorption layers 407 a provided on side ends of the ridge portion 308and ion-implanted light absorption layers 407 b provided on side ends ofan element separated from the ion-implanted light absorption layers 407a at prescribed intervals. The ion-implanted light absorption layers 407a have a width of about 1 μm, while the ion-implanted light absorptionlayers 407 b are arranged at intervals of about 1 μm from theion-implanted light absorption layers 407 a. The ion-implanted lightabsorption layers 407 are examples of the “light absorption layer” inthe present invention. Side ends of the ion-implanted light absorptionlayers 407 a closer to the ridge portion 308 are substantially arrangedimmediately under the side ends of the ridge portion 308. Thus, thewidth (width of optical confinement) W11 between the side ends of theion-implanted light absorption layers 407 a is substantially identicalto the width (width of current narrowing) (about 2 μm) of the ridgeportion 308.

A p-side ohmic electrode 309 is formed on the p-type contact layer 306constituting the ridge portion 308. An insulator film 410 of SiO₂ havinga thickness of about 200 nm is formed to cover the surfaces of thep-type cladding layer 305, the p-type contact layer 306 and the p-sideohmic electrode 309. This insulator film 410 has an opening 410 a on theupper surface of the p-side ohmic electrode 309. A p-side pad electrode411 consisting of a Ti layer having a thickness of about 100 nm, a Pdlayer having a thickness of about 100 nm and an Au layer having athickness of about 3 μm in ascending order is formed on a portion of theupper surface of the insulator film 410 located on the upper surface ofthe p-side ohmic electrode 309 to be in contact with the p-side ohmicelectrode 309 through the opening 410 a. An n-side electrode 312 isformed on the back surface of the n-type GaN substrate 301.

In a nitride semiconductor laser element according to the twenty-sixthembodiment, as hereinabove described, the ion-implanted light absorptionlayers 407 formed by ion implantation are so provided on regions of thep-type cladding layer 305 other than the projecting portion constitutingthe ridge portion 308 that the ion-implanted light absorption layers 407can be formed with excellent reproducibility due to excellentreproducibility of ion implantation. Thus, transverse opticalconfinement can be controlled with excellent reproducibility.Consequently, the transverse mode can be stabilized with excellentreproducibility while performing current narrowing through the ridgeportion 308. Further, the transverse mode can be so stabilized thatoutbreak of kinks (bending of current-light output characteristics)resulting from higher mode oscillation can be suppressed. Thus, a highermaximum light output can be obtained while the beam shape can bestabilized.

According to the twenty-sixth embodiment, further, the ion-implantedlight absorption layers 407 are provided dividedly into theion-implanted light absorption layers 407 a on the side ends of theridge portion 308 and the ion-implanted light absorption layers 407 b onthe side ends of the element so that regions formed with theion-implanted light absorption layers 407 can be inhibited fromincrease, whereby a portion in the vicinity of the MQW emission layer304 can be inhibited from excess light absorption. Consequently,increase of the threshold current can be suppressed.

A fabrication process for the nitride semiconductor laser elementaccording to the twenty-sixth embodiment is now described with referenceto FIGS. 124 to 128.

As shown in FIG. 125, the layers up to the striped (elongated) ridgeportion 308, constituted of the projecting portion of the p-typecladding layer 305 and the p-type contact layer 306, having the width ofabout 2 μm and the height of about 260 nm are formed through afabrication process similar to that of the twenty-first embodiment shownin FIGS. 101 to 103. Thereafter ion implantation masks 420 consisting ofSiO₂ films having a thickness of about 800 nm are formed on the p-sideohmic electrode 309 and prescribed regions of the surfaces of flatportions of the p-type cladding layer 305 other than the projectingportion. At this time, the ion implantation masks 420 located on thesurfaces of the flat portions of the p-type cladding layer 305 otherthan the projecting portion are formed to have a width of about 1 μm andto be arranged at intervals of about 1 μm from the side ends of theridge portion 308.

According to the twenty-sixth embodiment, the ion implantation masks 420are thereafter employed as masks for ion-implanting carbon (C), as shownin FIG. 126. Thus, the ion-implanted light absorption layers 407 havingthe ion implantation depth (thickness) of about 300 nm are formed overthe surfaces of the flat portions of the p-type cladding layer 305 otherthan the projecting portion to the MQW emission layer 304 and the n-typecladding layer 303. Ion implantation conditions for carbon areimplantation energy of about 95 keV, a dose of about 5×10¹³ cm⁻² and animplantation temperature of the room temperature. This ion implantationis performed from a direction inclined by about 70 in the longitudinaldirection of the p-side ohmic electrode 309. At this time, no ions areimplanted into regions corresponding to the ion implantation masks 420,whereby the ion-implanted light absorption layers 407 are formeddividedly into the ion-implanted light absorption layers 407 a on theside ends of the ridge portion 308 and the ion-implanted lightabsorption layers 407 b on the side ends of the element. Theion-implanted light absorption layers 407 a on the side ends of theridge portion 308 have the width of about 1 μm, while the side endscloser to the ridge portion 308 are substantially arranged immediatelyunder the side ends of the ridge portion 308. Therefore, the width(width of optical confinement) W11 between the side ends of theion-implanted light absorption layers 407 a reaches the size of about 2μm substantially identical to the width (width of current narrowing)(about 2 μm) of the ridge portion 308. Further, the ion-implanted lightabsorption layers 407 b are arranged at the intervals of about 1 μm fromof the ion-implanted light absorption layers 407 a.

Thereafter the ion implantation masks 420 are removed thereby obtainingthe state shown in FIG. 127.

As shown in FIG. 128, an SiO₂ film (not shown) having a thickness ofabout 200 nm is formed to cover the overall surface, and a prescribedregion of the SiO₂ film located on the upper surface of the p-side ohmicelectrode 309 is removed. Thus, the insulator film 410 consisting of theSiO₂ film, having the opening 410 a on the upper surface of the p-sideohmic electrode 309, having the thickness of about 200 nm is formed.

Finally, the p-side pad electrode 411 consisting of the Ti layer havingthe thickness of about 100 nm, the Pd layer having the thickness ofabout 100 nm and the Au layer having the thickness of about 3 μm inascending order is formed on the upper surface of the portion of theinsulator film 410 located on the upper surface of the p-side ohmicelectrode 309 to be in contact with the p-side ohmic electrode 309through the opening 410 a, as shown in FIG. 124. Further, the n-sideelectrode 312 is formed on the back surface of the n-type GaN substrate301. Thus, the nitride semiconductor laser element according to thetwenty-sixth embodiment is completed.

Twenty-Seventh Embodiment

Referring to FIG. 129, ion-implanted light absorption layers 437 ahaving an implantation depth (thickness) of about 150 nm are formed onside ends of a ridge portion 308 according to this twenty-seventhembodiment, in the structure of the aforementioned twenty-sixthembodiment. In other words, the ion-implanted light absorption layers437 a provided on the side ends of the ridge portion 308 do not reachthe interior of an MQW emission layer 304. These ion-implanted lightabsorption layers 437 a and ion-implanted absorption layers 437 bconstitute ion-implanted light absorption layers 437 according to thetwenty-seventh embodiment. The ion-implanted light absorption layers 437are examples of the “light absorption layer” in the present invention.

Side ends of the ion-implanted light absorption layers 437 a closer tothe ridge portion 308 are arranged on positions separated from the sideends of the ridge portion 308 by about 0.2 μm. Thus, the width (width ofoptical confinement) W12 between the side ends of the ion-implantedlight absorption layers 437 a is about 2.4 μm, which is larger than thewidth (width of current narrowing) (about 2 μm) of the ridge portion308. The ion-implanted light absorption layers 437 a have a width ofabout 0.8 μm, while the ion-implanted light absorption layers 437 b arearranged at intervals of about 1 μm from the ion-implanted lightabsorption layers 437 a. The remaining structure of the twenty-seventhembodiment is similar to that of the aforementioned twenty-sixthembodiment.

According to the twenty-seventh embodiment, as hereinabove described,the implantation depth (thickness) of the ion-implanted light absorptionlayers 437 a on the side ends of the ridge portion 308 is set to theimplantation depth (thickness) of about 150 nm so that the ion-implantedlight absorption layers 437 a do not reach the interior of the MQWactive layer 304, whereby light absorption in the vicinity of the MQWemission layer 304 can be further inhibited from excessiveness.Consequently, increase of a threshold current can be further suppressed.

The remaining effects of the twenty-seventh embodiment are similar tothose of the aforementioned twenty-sixth embodiment.

A fabrication process for a nitride semiconductor laser device accordingto the twenty-seventh embodiment is now described with reference toFIGS. 129 to 133.

As shown in FIG. 130, layers up to the striped (elongated) ridge portion308, constituted of a projecting portion of a p-type cladding layer 305and a p-type contact layer 360, having a width of about 2 μm and aheight of about 260 nm are formed through a fabrication process similarto that of the twenty-first embodiment shown in FIGS. 101 to 103.Thereafter an ion implantation mask 440 a consisting of an SiO₂ filmhaving a thickness of about 200 nm is formed on the upper surface andthe side surfaces of a p-side ohmic electrode 309, the side surfaces ofthe ridge portion 308 and prescribed regions of the surfaces of flatportions of the p-type cladding layer 305 other than the projectingportion. At this time, the ion implantation mask 440 a is so formed thatside ends of the ion implantation mask 440 a are arranged on positionsseparated by about 2 μm from the side ends of the ridge portion 308.Thereafter ion implantation masks 440 b consisting of SiO₂ films havinga thickness of about 600 nm and a width of about 1 μm are formed on sideend regions of the ion implantation mask 440 a. Thus, an ionimplantation mask 440 consisting of the ion implantation mask 440 a andthe ion implantation masks 440 b is formed. The thickness of side endregions (portions separated from the side ends of the ridge portion 308by about 2 μm) of the ion implantation mask 440 is about 800 μm.

According to the twenty-seventh embodiment, the ion implantation mask440 is employed as a mask for ion-implanting carbon (C) thereby formingthe ion-implanted light absorption layers 437, as shown in FIG. 131. Ionimplantation conditions for carbon are implantation energy of about 95keV, a dose of about 5×10¹³ cm⁻² and an implantation temperature of theroom temperature. This ion implantation is performed from a directioninclined by about 70 in the longitudinal direction of the p-side ohmicelectrode 309. At this time, no ions are implanted into regionscorresponding to the side end regions of the ion implantation mask 440having the large thickness (about 800 nm), whereby the ion-implantedlight absorption layers 437 are formed dividedly into the ion-implantedlight absorption layers 437 a on the side ends of the ridge portion 308and the ion-implanted light absorption layers 437 b on the side ends ofthe element.

No ions are implanted into regions corresponding to portions of the ionimplantation mask layer 440 formed on the side surfaces of the ridgeportion 308 and the p-side ohmic electrode 309 either. Further, theregions of the ion implantation mask 440 other than the side ends have asmall thickness (about 200 nm), whereby ions are implanted into regionscorresponding to the regions of the ion implantation mask 440 other thanthe side ends. However, the ion implantation depth is reduced ascompared with the regions formed with no ion implantation mask 440.

Thus, the ion-implanted light absorption layers 437 a provided on theside ends of the ridge portion 308 have the width of about 0.8 μm, whilethe side ends closer to the ridge portion 308 are arranged on thepositions separated from the side ends of the ridge portion 308 by about0.2 μm. Therefore, the width (width of optical confinement) W12 betweenthe side ends of the ion-implanted light absorption layers 437 a isabout 2.4 μm, which is larger than the width (width of currentnarrowing) (about 2 μm) of the ridge portion 308. Further, theion-implanted light absorption layers 437 b are arranged at theintervals of about 1 μm from the ion-implanted light absorption layers437 a. The ion implantation depth (thickness) of the ion-implanted lightabsorption layers 437 a is about 150 nm, and the ion implantation depth(thickness) of the ion-implanted light absorption layers 437 b is about300 nm.

Thereafter the ion implantation mask layer 440 is removed therebyobtaining the state shown in FIG. 132.

As shown in FIG. 133, an insulator film 410 having an opening 410 a onthe upper surface of the p-side ohmic electrode 309 is formed through aprocess similar to that of the twenty-sixth embodiment shown in FIG.128.

Finally, a p-side pad electrode 411 is formed on the upper surface of aportion of the insulator film 410 located on the upper surface of thep-side ohmic electrode 309 to be in contact with the upper surface ofthe p-side ohmic electrode 309 through the opening 410 a. Further, ann-side electrode 312 is formed on the back surface of an n-type GaNsubstrate 301. Thus, a nitride semiconductor laser element according tothe twenty-seventh embodiment is completed.

Twenty-Eighth Embodiment

Referring to FIG. 134, an example of rendering the width (width ofoptical confinement) between side ends of ion-implanted light absorptionlayers larger than the width (width of current narrowing) of a ridgeportion in the structure of the aforementioned twenty-sixth embodimentis described with reference to this twenty-eighth embodiment. Theremaining structure of the twenty-eighth embodiment is similar to thatof the aforementioned twenty-sixth embodiment.

Referring to FIG. 134, a projecting portion of a p-type cladding layer305 and a p-type contact layer 306 constitute a striped (elongated)ridge portion 308 having a width of about 2 μm and a height of about 260nm according to this twenty-eighth embodiment, similarly to theaforementioned twenty-sixth embodiment.

According to the twenty-eighth embodiment, ion-implanted lightabsorption layers 457, formed by ion-implanting carbon (C), having animplantation depth (thickness) of about 300 nm are provided. Theseion-implanted light absorption layers 457 are provided dividedly intoion-implanted light absorption layers 457 a provided on side ends of theridge portion 308 and ion-implanted light absorption layers 457 bprovided on side ends of an element. The ion-implanted light absorptionlayers 457 are examples of the “light absorption layer” in the presentinvention. Side ends of the ion-implanted light absorption layers 457 acloser to the ridge portion 308 are arranged on positions separated fromthe side ends of the ridge portion 308 by about 1 μm. Thus, the width(width of optical confinement) W13 between the side ends of theion-implanted light absorption layers 457 a is about 4 μm, which islarger than the width (width of current narrowing) (about 2 μm) of theridge portion 308. Further, the ion-implanted light absorption layers457 a have a width of about 1 μm, while the ion-implanted lightabsorption layers 457 b are arranged at intervals of about 1 μm from theion-implanted light absorption layers 457 a.

A p-side ohmic electrode 309 is formed on the p-type contact layer 306constituting the ridge portion 308. An insulator film 410 is formed tocover the surfaces of the p-type cladding layer 305, the p-type contactlayer 306 and the p-side ohmic electrode 309. This insulator film 410has an opening 410 a on the upper surface of the p-side ohmic electrode309. A p-side pad electrode 411 is formed on the upper surface of theinsulator film 410 to be in contact with the upper surface of the p-sideohmic electrode 309 through the opening 410 a. An n-side electrode 312is formed on the back surface of an n-type GaN substrate 301.

According to the twenty-eighth embodiment, as hereinabove described, thewidth (width of optical confinement) W13 between the side ends of theion-implanted light absorption layers 457 a closer to the side ends ofthe ridge portion 308 is set to about 4 μm which is larger than thewidth (width of current narrowing) (about 2 μm) of the ridge portion308, whereby light absorption in the vicinity of the MQW emission layer304 can be inhibited from excessiveness. Further, the ion-implantedlight absorption layers 457 are provided dividedly into theion-implanted light absorption layers 457 a on the side ends of theridge portion 308 and the ion-implanted light absorption layers 457 b onthe side ends of the element so that regions for forming theion-implanted light absorption layers 457 can be inhibited fromincrease, whereby light absorption in the vicinity of the MQW emissionlayer 304 can be inhibited from excessiveness also by this.Consequently, increase of a threshold current can be further suppressed.

The remaining effects of the twenty-eighth embodiment are similar tothose of the aforementioned twenty-sixth embodiment.

A fabrication process for a nitride semiconductor laser elementaccording to the twenty-eighth embodiment is now described withreference to FIGS. 135 to 138.

First, the layers up to the striped (elongated) ridge portion 308,constituted of the projecting portion of the p-type cladding layer 305and the p-type contact layer 306, having the width of about 2 μm and theheight of about 260 nm are formed as shown in FIG. 135 through afabrication process similar to that of the twenty-first embodiment shownin FIGS. 101 to 103. Thereafter ion implantation masks 460 consisting ofSiO₂ films having a thickness of about 800 nm are formed on the uppersurface and the side surfaces of the p-side ohmic electrode 309, theside surfaces of the ridge portion 308 and prescribed regions of thesurfaces of flat portions of the p-type cladding layer 305 other thanthe projecting portion. At this time, the ion implantation masks 460located on the surfaces of the flat portions of the p-type claddinglayer 305 other than the projecting portion are formed to have a widthof about 1 μm and to be arranged in a cycle of about 2 μm at intervalsof about 1 μm. Further, the ion implantation masks 460 located on thesurfaces of the flat portions of the p-type cladding layer 305 otherthan the projecting portion are so formed that the side ends thereof arearranged on positions separated from the side ends of the ridge portion308 by about 3 μm.

According to the twenty-eighth embodiment, the ion implantation masks460 are thereafter employed as masks for ion-implanting carbon (C), asshown in FIG. 136. Thus, the ion-implanted light absorption layers 457having the ion implantation depth (thickness) of about 300 nm are formedover the surfaces of the flat portions of the p-type cladding layer 305other than the projecting portion to the MQW emission layer 304 and then-type cladding layer 303. Ion implantation conditions for carbon areimplantation energy of about 95 keV, a dose of about 5×10¹³ cm⁻² and animplantation temperature of the room temperature. This ion implantationis performed from a direction inclined by about 70 in the longitudinaldirection of the p-side ohmic electrode 309. At this time, no ions areimplanted into regions corresponding to the ion implantation masks 460,whereby the ion-implanted light absorption layers 457 are formeddividedly into the ion-implanted light absorption layers 457 a on theside ends of the ridge portion 308 and the ion-implanted lightabsorption layers 457 b on the side ends of the element. Theion-implanted light absorption layers 457 a on the side ends of theridge portion 308 have the width of about 1 μm, while the side endscloser to the ridge portion 308 are arranged on the positions separatedfrom the side ends of the ridge portion 308 by about 1 μm. Thus, thewidth (width of optical confinement) W13 between the side ends of theion-implanted light absorption layers 457 a is about 4 μm, which islarger than the width (width of current narrowing) (about 2 μm) of theridge portion 308. Further, the ion-implanted light absorption layers457 b are arranged at the intervals of about 1 μm from of theion-implanted light absorption layers 457 a.

Thereafter the ion implantation masks 460 are removed thereby obtainingthe state shown in FIG. 137.

As shown in FIG. 138, the insulator film 410 having the opening 410 a onthe upper surface of the p-side ohmic electrode 309 is formed through aprocess similar to that of the twenty-sixth embodiment shown in FIG.128.

Finally, the p-side pad electrode 411 is formed on the upper surface ofthe portion of the insulator film 410 located on the upper surface ofthe p-side ohmic electrode 309 to be in contact with the upper surfaceof the p-side ohmic electrode 309 through the opening 410 a, as shown inFIG. 134. Further, the n-side electrode 312 is formed on the backsurface of the n-type GaN substrate 301. Thus, the nitride semiconductorlaser element according to the twenty-eighth embodiment is completed.

Twenty-Ninth Embodiment

Referring to FIG. 139, an example of dividing ion-implanted lightabsorption layers provided between side ends of a ridge portion and sideends of an element into three types of ion-implanted light absorptionlayers dissimilarly to the aforementioned twenty-sixth to twenty-eighthembodiments is described with reference to this twenty-ninth embodiment.The remaining structure of the twenty-ninth embodiment is similar tothat of the aforementioned twenty-eighth embodiment.

Referring to FIG. 139, a projecting portion of a p-type cladding layer305 and a p-type contact layer 306 constitute a striped (elongated)ridge portion 308 having a width of about 2 μm and a height of about 260nm according to this twenty-ninth embodiment, similarly to thetwenty-eighth embodiment.

According to the twenty-ninth embodiment, ion-implanted light absorptionlayers 477, formed by ion-implanting carbon (C), having an implantationdepth (thickness) of about 300 nm are provided. These ion-implantedlight absorption layers 477 are provided dividedly into ion-implantedlight absorption layers 477 a provided on side ends of the ridge portion308, ion-implanted light absorption layers 477 b provided on side endsof an element and ion-implanted light absorption layers 477 c providedbetween the ion-implanted light absorption layers 477 a and theion-implanted light absorption layers 477 b. The ion-implanted lightabsorption layers 477 are examples of the “light absorption layer” inthe present invention. Side ends of the ion-implanted light absorptionlayers 477 a closer to the ridge portion 308 are arranged on positionsseparated from the side ends of the ridge portion 308 by about 1 μm.Thus, the width (width of optical confinement) W14 between the side endsof the ion-implanted light absorption layers 477 a is about 4 μm, whichis larger than the width (width of current narrowing) (about 2 μm) ofthe ridge portion 308. Further, the ion-implanted light absorptionlayers 477 a and 477 c have a width of about 1 μm. The ion-implantedlight absorption layers 477 c are arranged at intervals of about 1 μmfrom the ion-implanted light absorption layers 477 a, while theion-implanted light absorption layers 477 b are arranged at intervals ofabout 1 μm from the ion-implanted light absorption layers 477 c.

A p-side ohmic electrode 309 is formed on the p-type contact layer 306constituting the ridge portion 308. Further, an insulator film 410 isformed to cover the surfaces of the p-type cladding layer 305, thep-type contact layer 306 and the p-side ohmic electrode 309. Thisinsulator film 410 has an opening 410 a on the upper surface of thep-side ohmic electrode 309. A p-side pad electrode 411 is formed on theupper surface of the insulator film 410 to be in contact with the uppersurface of the p-side ohmic electrode 309 through the opening 410 a. Ann-side electrode 312 is formed on the back surface of an n-type GaNsubstrate 301.

According to the twenty-eighth embodiment, as hereinabove described, thewidth (width of optical confinement) W14 between the side ends of theion-implanted light absorption layers 477 a closer to the side ends ofthe ridge portion 308 is set to about 4 μm which is larger than thewidth (about 2 μm) of the ridge portion 308, whereby light absorption inthe vicinity of an MQW emission layer 304 can be inhibited fromexcessiveness. Further, the ion-implanted light absorption layers 477provided between the side ends of the ridge portion 308 and the sideends of the element are so divided into the three types of ion-implantedlight absorption layers 477 a, 477 b and 477 c that regions formed withthe ion-implanted light absorption layers 477 can be further inhibitedfrom increase as compared with the aforementioned twenty-eighthembodiment, whereby the light absorption in the vicinity of the MQWemission layer 304 can be further inhibited from excessiveness.Consequently, increase of a threshold current can be further suppressedas compared with the twenty-eighth embodiment.

The remaining effects of the twenty-ninth embodiment are similar tothose of the aforementioned twenty-sixth embodiment.

A fabrication process for a nitride semiconductor laser elementaccording to the twenty-ninth embodiment is now described with referenceto FIGS. 139 to 143.

First, the layers up to the striped (elongated) ridge portion 308,constituted of the projecting portion of the p-type cladding layer 305and the p-type contact layer 306, having the width of about 2 μm and theheight of about 260 nm are formed as shown in FIG. 140 through afabrication process similar to that of the twenty-first embodiment shownin FIGS. 101 to 103. Thereafter ion implantation masks 480 consisting ofSiO₂ films having a thickness of about 800 nm are formed on the uppersurface and the side surfaces of the p-side ohmic electrode 309, theside surfaces of the ridge portion 308 and prescribed regions of thesurfaces of flat portions of the p-type cladding layer 305 other thanthe projecting portion. At this time, the ion implantation masks 480located on the surfaces of the flat portions of the p-type claddinglayer 305 other than the projecting portion are formed to have a widthof about 1 μm and to be arranged in a cycle of about 2 μm at intervalsof about 1 μm. Further, the ion implantation masks 480 located on thesurfaces of the flat portions of the p-type cladding layer 305 otherthan the projecting portion are so formed that the side ends thereof arearranged on positions separated from the side ends of the ridge portion308 by about 5 μm.

According to the twenty-ninth embodiment, the ion implantation masks 480are thereafter employed as masks for ion-implanting carbon (C), as shownin FIG. 141. Thus, the ion-implanted light absorption layers 477 havingthe ion implantation depth (thickness) of about 300 nm are formed overthe surfaces of the flat portions of the p-type cladding layer 305 otherthan the projecting portion to the MQW emission layer 304 and an n-typecladding layer 303. Ion implantation conditions for carbon areimplantation energy of about 95 keV, a dose of about 5×10¹³ cm⁻² and animplantation temperature of the room temperature. This ion implantationis performed from a direction inclined by about 70 in the longitudinaldirection of the p-side ohmic electrode 309. At this time, no ions areimplanted into regions corresponding to the ion implantation masks 480,whereby the ion-implanted light absorption layers 477 are formeddividedly into the ion-implanted light absorption layers 477 a on theside ends of the ridge portion 308, the ion-implanted light absorptionlayers 477 b on the side ends of the element and the ion-implanted lightabsorption layers 477 c provided between the ion-implanted lightabsorption layers 477 a and the ion-implanted light absorption layers477 b. The ion-implanted light absorption layers 477 a provided on theside ends of the ridge portion 308 have the width of about 1 μm, whilethe side ends closer to the ridge portion 308 are arranged on thepositions separated from the side ends of the ridge portion 308 by about1 μm. Thus, the width (width of optical confinement) W14 between theside ends of the ion-implanted light absorption layers 477 a is about 4μm, which is larger than the width (width of current narrowing) (about 2μm) of the ridge portion 308. Further, the ion-implanted lightabsorption layers 477 c are arranged at the intervals of about 1 μm fromof the ion-implanted light absorption layers 477 a, while theion-implanted light absorption layers 477 b are arranged at theintervals of about 1 μm from of the ion-implanted light absorptionlayers 477 c.

Thereafter the ion implantation masks 480 are removed thereby obtainingthe state shown in FIG. 142.

As shown in FIG. 143, the insulator film 410 having the opening 410 a onthe upper surface of the p-side ohmic electrode 309 is formed through aprocess similar to that of the twenty-sixth embodiment shown in FIG.128.

Finally, the p-side pad electrode 411 is formed on the upper surface ofthe portion of the insulator film 410 located on the upper surface ofthe p-side ohmic electrode 309 to be in contact with the p-side ohmicelectrode 309 through the opening 410 a, as shown in FIG. 139. Further,the n-side electrode 312 is formed on the back surface of the n-type GaNsubstrate 301. Thus, the nitride semiconductor laser element accordingto the twenty-ninth embodiment is completed.

Thirtieth Embodiment

Referring to FIG. 144, ion-implanted light absorption layers 497 ahaving an implantation depth (thickness) of about 150 nm are formed onside ends of a ridge portion 308 according to this thirtieth embodiment,in the structure of the aforementioned twenty-eighth embodiment. Inother words, the ion-implanted light absorption layers 497 a provided onthe side ends of the ridge portion 308 do not reach the interior of anMQW emission layer 304. These ion-implanted light absorption layers 497a and ion-implanted absorption layers 497 b constitute ion-implantedlight absorption layers 497 of the thirtieth embodiment. Theion-implanted light absorption layers 497 are examples of the “lightabsorption layer” in the present invention.

Side ends of the ion-implanted light absorption layers 497 a closer tothe ridge portion 308 are arranged on positions separated from side endsof the ridge portion 308 by about 1 μm. Thus, the width (width ofoptical confinement) W15 between the side ends of the ion-implantedlight absorption layers 497 a is about 4 μm, which is larger than thewidth (width of current narrowing) (about 2 μm) of the ridge portion308. Further, the ion-implanted light absorption layers 497 a have awidth of about 1 μm, while the ion-implanted light absorption layers 497b are arranged at intervals of about 1 μm from the ion-implanted lightabsorption layers 497 a. The remaining structure of the thirtiethembodiment is similar to that of the aforementioned twenty-eighthembodiment.

According to the thirtieth embodiment, as hereinabove described, theimplantation depth (thickness) of the ion-implanted light absorptionlayers 497 a on the side ends of the ridge portion 308 is so set to theimplantation depth (thickness) of about 150 nm that the ion-implantedlight absorption layers 497 a do not reach the interior of the MQWactive layer 304, whereby light absorption in the vicinity of the MQWemission layer 304 can be further inhibited from excessiveness.Consequently, increase of a threshold current can be further suppressed.

The remaining effects of the thirtieth embodiment are similar to thoseof the aforementioned twenty-eighth embodiment.

A fabrication process for a nitride semiconductor laser elementaccording to the thirtieth embodiment is now described with reference toFIGS. 144 to 148.

First, layers up to the striped (elongated) ridge portion 308,constituted of a projecting portion of a p-type cladding layer 305 and ap-type contact layer 306, having a width of about 2 μm and a height ofabout 260 nm are formed through a fabrication process similar to that ofthe twenty-first embodiment shown in FIGS. 101 to 103, as shown in FIG.145. Thereafter an ion implantation mask 500 a of an SiO₂ film having athickness of about 200 nm is formed on the upper surface and the sidesurfaces of a p-side ohmic electrode 309, the side surfaces of the ridgeportion 308 and prescribed regions on the surfaces of flat portions ofthe p-type cladding layer 305 other than the projecting portion. At thistime, the ion implantation mask 500 a is so formed that the side endsthereof are arranged on positions separated from the side ends of theridge portion 308 by about 3 μm. Thereafter other ion implantation masks500 b of SiO₂ films having a thickness of about 600 nm are formed onprescribed regions of the ion implantation mask 500 a located on thesurfaces of the flat portions of the p-type cladding layer 305 otherthan the projecting portion. More specifically, the ion implantationmasks 500 b located on side end regions of the ion implantation mask 500a are formed with a width of about 1 μm while the ion implantation masks500 b located on regions of the ion implantation mask 500 a closer tothe ridge portion 308 are formed with a width of about 0.8 μm. Thus, anion implantation mask 500 consisting of the ion implantation mask 500 aand the ion implantation masks 500 b is formed. The thicknesses of sideend regions (portions separated from the side ends of the ridge portion308 by about 3 μm) of the ion implantation mask 500 and regions of theion implantation mask 500 closer to the ridge portion 308 are about 800μm.

According to the thirtieth embodiment, the ion implantation mask 500 isthereafter employed as a mask for ion-implanting carbon (C), therebyforming the ion-implanted light absorption layers 497 as shown in FIG.146. Ion implantation conditions for carbon are implantation energy ofabout 95 keV, a dose of about 5×10¹³ cm⁻² and an implantationtemperature of the room temperature. This ion implantation is performedfrom a direction inclined by about 70 in the longitudinal direction ofthe p-side ohmic electrode 309. At this time, no ions are implanted intothe regions corresponding to the side end regions of the ionimplantation mask 500 having the large thickness (about 800 nm), wherebythe ion-implanted light absorption layers 500 are formed dividedly intothe ion-implanted light absorption layers 497 a on the side ends of theridge portion 308 and the ion-implanted light absorption layers 497 b onthe side ends of the element.

Further, no ions are implanted into the regions corresponding to theregions, having the large thickness (about 800 nm), of the ionimplantation mask 500 closer to the ridge portion 308 either. Inaddition, the regions of the ion implantation mask 500 other than theside ends have the small thickness (about 200 nm), whereby ions areimplanted into the regions corresponding to the regions of the ionimplantation mask 500 other than the side ends. However, the ionimplantation depth is smaller as compared with the regions formed withno ion implantation mask 500.

Thus, the ion-implanted light absorption layers 497a provided on theside ends of the ridge portion 308 have the width of about 1 μm, and theside ends closer to the ridge portion 308 are arranged on the positionsseparated from the side ends of the ridge portion 308 by about 1 μm.Therefore, the width (width of optical confinement) W15 between the sideends of the ion-implanted light absorption layer 497 a is about 4 μm,which is larger than the width (width of current narrowing) (about 2 μm)of the ridge portion 308. Further, the ion-implanted light absorptionlayers 497 b are arranged at the intervals of about 1 μm from theion-implanted light absorption layers 497 a. The ion implantation depth(thickness) of the ion-implanted light absorption layers 497 a is about150 nm, while the ion implantation depth (thickness) of theion-implanted light absorption layers 497 b is about 300 nm.

Thereafter the ion implantation mask layer 500 is removed, therebyobtaining the state shown in FIG. 147.

As shown in FIG. 148, an insulator film 410 having an opening 410 a onthe upper surface of the p-side ohmic electrode 309 is formed through aprocess similar to that of the twenty-sixth embodiment shown in FIG.128.

Finally, a p-side pad electrode 411 is formed on the upper surface ofthe portion of the insulator film 410 located on the upper surface ofthe p-side ohmic electrode 309 to be in contact with the upper surfaceof the p-side ohmic electrode 309 through the opening 410 a, as shown inFIG. 144. Further, an n-side electrode 312 is formed on the back surfaceof an n-type GaN substrate 301. Thus, the nitride semiconductor laserelement according to the thirtieth embodiment is completed.

Thirty-First Embodiment

Referring to FIGS. 149 to 153, an example of varying the width (width ofoptical confinement) between side ends of ion-implanted light absorptionlayers with a portion closer to a cavity end surface of an element and aportion closer to the central portion is described with reference tothis thirty-first embodiment.

According to this thirty-first embodiment, an n-type buffer layer 602 ofn-type GaN doped with Si having a thickness of about 1 μm is formed onan n-type GaN substrate 601, as shown in FIG. 149. An n-type claddinglayer 603 of n-type Al_(0.07)Ga_(0.03)N doped with Si having. athickness of about 1 μm is formed on the n-type buffer layer 602. Then-type buffer layer 602 and the n-type cladding layer 603 are examplesof the “first nitride semiconductor layer” in the present invention.

An MQW emission layer 604 is formed on the n-type cladding layer 603.This MQW emission layer 604 is constituted of an n-type light guidelayer 604 a, an MQW active layer 604 b, an undoped light guide layer 604c and an undoped cap layer 604 d, as shown in FIG. 150. The n-type lightguide layer 604 a is formed on the n-type cladding layer 603 (see FIG.149), and consists of n-type In_(0.1)Ga_(0.9)N doped with Si having athickness of about 0.1 μm. The MQW active layer 604 b, formed on then-type light guide layer 604 a, has a structure obtained by alternatelystacking four barrier layers 604 e of undoped In_(0.02)Ga_(0.08)N eachhaving a thickness of about 8 nm and three well layers 604 f of undopedIn_(0.15)Ga_(0.85)N each having a thickness of about 3.5 nm. The undopedlight guide layer 604 c, formed on the MQW active layer 604 b, consistsof undoped In_(0.1)Ga_(0.9)N having a thickness of about 0.1 μm. Theundoped cap layer 604 d, formed on the undoped light guide layer 604 c,consists of Al_(0.15)Ga_(0.85)N having a thickness of about 20 nm.

As shown in FIG. 149, a p-type cladding layer 605 having a projectingportion and consisting of p-type Al_(0.07)Ga_(0.03)N doped with Mghaving a thickness of about 0.4 μm is formed on the MQW emission layer604. The thickness of the projecting portion of this p-type claddinglayer 605 is about 0.35 μm, and the thickness of flat portions otherthan the projecting portion is about 0.05 μm. A p-type contact layer 606of p-type GaN doped with Mg having a thickness of about 20 nm is formedon the projecting portion of the p-type cladding layer 605. Theprojecting portion of the p-type cladding layer 605 and the p-typecontact layer 606 constitute a striped (elongated) ridge portion 608.The p-type cladding layer 605 and the p-type contact layer 606 areexamples of the “second nitride semiconductor layer” in the presentinvention.

According to the thirty-first embodiment, ion-implanted light absorptionlayers 607 formed by ion-implanting carbon (C) are provided. Theseion-implanted light absorption layers 607 have an implantation depth(about 0.4 μm) reaching the interior of the n-type cladding layer 603from the surfaces of the flat portions of the p-type cladding layer 605other than the projecting portion. The ion-implanted light absorptionlayers 607 are examples of the “light absorption layer” in the presentinvention. The width (width of optical confinement) between side ends ofthese ion-implanted light absorption layers 607 varies with portionsclose to a cavity end surface of an element and portions close to thecentral portion. More specifically, the width W21 between the side endsof portions of the ion-implanted light absorption layers 607 located inthe vicinity of the cavity end surface of the element has a size (about1.5 μm) substantially identical to the width (width of currentnarrowing) of the ridge portion 608, as shown in FIGS. 151 and 153. Asshown in FIGS. 152 and 153, the width W22 between the side ends ofportions of the ion-implanted light absorption layers 607 located in thevicinity of the central portion of the element has a size (about 7.5 μm)larger than the width (width of current narrowing) of the ridge portion608. In other words, the width W21 (about 1.5 μm) between the side endsof the portions of the ion-implanted light absorption layers 607 locatedin the vicinity of the cavity end surface of the element has a smallersize than the width W22 (about 7.5 μm) between the side ends of theportions of the ion-implanted light absorption layers 607 located in thevicinity of the central portion of the element. As shown in FIG. 153,boundary regions between the portions of the ion-implanted lightabsorption layers 607 located in the vicinity of the cavity end surfaceof the element and the portions of the ion-implanted light absorptionlayers 607 located in the vicinity of the central portion of the elementare formed in tapered shapes so that the width thereof is graduallychanged. As to the detailed planar shape of the ion-implanted lightabsorption layers 607, the length L1 of the portions located in thevicinity of the cavity end surface of the element is about 20 μm, thelength L2 of the portions located in the vicinity of the central portionof the element is about 500 μm and the length L3 of the tapered portionsis about 30 μm.

As shown in FIG. 149, a p-side ohmic electrode 609 consisting of a Ptlayer having a thickness of about 1 nm and a Pd layer having a thicknessof about 20 nm in ascending order is formed on the p-type contact layer606 constituting the ridge portion 608. Further, insulator films 610 ofSiO₂ having a thickness of about 100 nm to about 300 nm are formed onthe surface of the p-type cladding layer 605 and the side surfaces ofthe p-type contact layer 606 and the p-side ohmic electrode 609. Ap-side pad electrode 611 consisting of a Ti layer having a thickness ofabout 100 nm, a Pd layer having a thickness of about 100 nm and an Aulayer having a thickness of about 300 nm in ascending order is formed onthe upper surfaces of the insulator films 610 to be in contact with theupper surface of the p-side ohmic electrode 609. An n-side electrode 612consisting of an Al layer having a thickness of about 6 nm, a Pd layerhaving a thickness of about 10 nm and an Au layer having a thickness ofabout 300 nm from the side closer to the back surface of the n-type GaNsubstrate 601 is formed on the back surface of the n-type GaN substrate601.

According to the thirty-first embodiment, as hereinabove described, theion-implanted light absorption layers 607 formed by ion implantation areso provided on the regions of the p-type cladding layer 605 other thanthe projecting portion constituting the ridge portion 608 that theion-implanted light absorption layers 607 can be formed with excellentreproducibility since ion implantation is excellent in reproducibility.Further, the width W21 between the side ends of the portions of theion-implanted light absorption layers 607 located in the vicinity of thecavity end surface of the element is rendered smaller than the width W22between the side ends of the portions of the ion-implanted lightabsorption layers 607 located in the vicinity of the central portion ofthe element so that transverse optical confinement can be excellentlyperformed on the cavity end surface of the element, whereby thetransverse mode can be stabilized. Thus, outbreak of kinks (bending ofcurrent-light output characteristics) resulting from higher modeoscillation can be suppressed. Further, light absorption in the vicinityof the MQW emission layer can be inhibited from excessiveness at thecentral portion of the element, whereby increase of a threshold currentcan be suppressed. Consequently, the beam shape can be stabilized whilesuppressing increase of the threshold current, reduction of slopeefficiency and reduction of the kink level.

According to the thirty-first embodiment, further, the boundary regionsbetween the portions of the ion-implanted light absorption layers 607located in the vicinity of the cavity end surface of the element and theportions of the ion-implanted light absorption layers 607 located in thevicinity of the central portion of the element are formed in the taperedshapes so that the width thereof is gradually changed, whereby abruptchange of light absorption can be suppressed. Thus, coupling lossbetween portions close to the cavity end surface of the element andportions close to the central portion of the element can be sosuppressed that reduction of output characteristics can be suppressed.Further, the boundary regions between the portions of the ion-implantedlight absorption layers 607 located in the vicinity of the cavity endsurface of the element and the portions of the ion-implanted lightabsorption layers 607 located in the vicinity of the central portion ofthe element are so formed in the tapered shapes that the width of theboundary regions between the portions of the ion-implanted lightabsorption layers 607 located in the vicinity of the cavity end surfaceof the element and the portions of the ion-implanted light absorptionlayers 607 located in the vicinity of the central portion of the elementcan be easily gradually changed.

A fabrication process for a nitride semiconductor laser elementaccording to the thirty-first embodiment is now described with referenceto FIGS. 149, 150 and 154 to 164.

As shown in FIG. 154, the n-type buffer layer 602 of n-type GaN dopedwith Si having the thickness of about 1 μm and the n-type cladding layer603 of n-type Al_(0.07)Ga_(0.03)N doped with Si having the thickness ofabout 1 μm are successively grown on the n-type GaN substrate 601 byMOCVD.

As shown in FIG. 150, the n-type light guide layer 604 a of n-typeIn_(0.1)Ga_(0.9)N doped with Si having the thickness of about 0.1 μm andthe MQW active layer 604 b are thereafter successively grown on then-type cladding layer 603 (see FIG. 154). In order to grow the MQWactive layer 604 b, the four barrier layers 604 e of undopedIn_(0.02)Ga_(0.08)N each having the thickness of about 8 nm and thethree well layers 604 f of undoped In_(0.15)Ga_(0.85)N each having thethickness of about 3.5 nm are alternately stacked. Then, the undopedlight guide layer 604 c of undoped In_(0.1)Ga_(0.9)N having thethickness of about 0.1 μm and the undoped cap layer 604 d ofAl_(0.15)Ga_(0.85)N having the thickness of about 20 nm are successivelygrown on the MQW active layer 604 b. Thus, the MQW emission layer 604consisting of the n-type light guide layer 604 a, the MQW active layer604 b, the undoped light guide layer 604 c and the undoped cap layer 604d is formed.

As shown in FIG. 154, the p-type cladding layer 605 consisting of p-typeAl_(0.07)Ga_(0.03)N doped with Mg having the thickness of about 0.4 μmand the p-type contact layer 606 of p-type GaN doped with Mg having thethickness of about 20 nm are successively grown on the MQW emissionlayer 604.

As shown in FIG. 155, the p-side ohmic electrode 609 consisting of thePt layer having the thickness of about 1 nm and the Pd layer having thethickness of about 20 nm in ascending order is formed on the p-typecontact layer 606 by electron beam evaporation. Thereafter an SiO₂ film613 having a thickness of about 200 μm to about 500 μm is formed on thep-side ohmic electrode 609 by plasma CVD or electron beam evaporation.This SiO₂ film 613 is employed as an etching mask in a step describedlater. Therefore, the SiO₂ film 613 is preferably formed by plasma CVDallowing formation of an excellent film.

As shown in FIG. 156, a positive resist film 614 having a thickness ofabout 0.5 μm to about 1 μm is formed on a prescribed region of the SiO₂film 613 in a striped (elongated) shape.

As shown in FIG. 157, the positive resist film 614 is employed as a maskfor removing prescribed regions of the p-side ohmic electrode 609 andthe SiO₂ film 613 by reactive ion etching (RIE: Reactive Ion Etching)with CF₄ gas. Etching conditions are a gas flow rate of about 10 sccm, apressure of about 0.13 Pa and power of about 200 W. Thereafter thepositive resist film 614 is removed through a resist stripper, therebyobtaining the state shown in FIG. 158.

As shown in FIG. 159, the SiO₂ film 613 is employed as a mask forpartially removing the p-type contact layer 606 and the p-type claddinglayer 605 by a thickness of about 0.35 μm from the upper surfaces byreactive ion etching with CF₄ gas. Thus, the striped (elongated) ridgeportion 608 constituted of the projecting portion of the p-type claddinglayer 605 and the p-type contact layer 606 is formed.

As shown in FIG. 160, an ion implantation mask 615 of positive resisthaving a thickness of about 1 μm is formed on prescribed regions of theupper surface and the side surfaces of the SiO₂ film 613, the sidesurfaces of the p-side ohmic electrode 609 and the ridge portion 608 andthe surfaces of flat portions of the p-type cladding layer 605 otherthan the projecting portion. At this time, the length L1 of the ionimplantation mask 615 from the cavity end surface of the element is setto about 20 μm, while the length L2 of a portion of the ion implantationmask 615 in the vicinity of the central portion of the element is set toabout 500 μm. Further, the boundary region between the portion of theion implantation mask 615 located in the vicinity of the cavity endsurface of the element and the portion of the ion implantation mask 615located in the vicinity of the central portion of the element is formedin a tapered shape so that the width thereof is gradually changed, whilethe length L3 of the tapered portion is set to about 30 μm. In addition,the width of the portion of the ion implantation mask 615 close to thecentral portion of the element is set to the width W22 (about 7.5 μm).

According to the thirty-first embodiment, the ion implantation mask 615is thereafter employed as a mask for ion-implanting carbon (C), as shownin FIG. 161. Ion implantation conditions for carbon are implantationenergy of about 95 keV, a dose of about 5×10¹³ cm⁻² and an implantationtemperature of the room temperature. This ion implantation is performedfrom a direction inclined by about 70 in the longitudinal direction ofthe p-side ohmic electrode 609. Thus, the ion-implanted light absorptionlayers 607 having the ion implantation depth (thickness) reaching theinterior of the n-type cladding layer 603 from the surfaces of the flatportions of the p-type cladding layer 605 other than the projectingportion are formed. The width W21 between the side ends of the portionsof the ion-implanted light absorption layers 607 located in the vicinityof the cavity end surface of the element reaches the size (about 1.5 μm)substantially identical to the width (width of current narrowing) of theridge portion 608, while the width W22 between the side ends of theportions of the ion-implanted light absorption layers 607 located in thevicinity of the central portion of the element reaches the size (about7.5 μm) larger than the width (width of current narrowing) of the ridgeportion 608. Further, the boundary regions between the portions of theion-implanted light absorption layers 607 located in the vicinity of thecavity end surface of the element and the portions of the ion-implantedlight absorption layers 607 located in the vicinity of the centralportion of the element are formed in the tapered shapes so that thewidth thereof is gradually changed.

Then, the ion implantation mask 615 is removed through a resiststripper. Thereafter the ion implantation mask 615 is completely removedby ashing with plasma. Thus, the state shown in FIG. 162 is obtained.

As shown in FIG. 163, the insulator film 610 of SiO₂ having thethickness of about 100 nm to about 300 nm is formed to cover the overallsurface.

As shown in FIG. 164, the portion of the insulator film 610 located onthe upper surface of the p-side ohmic electrode 609 is removed.

Finally, the p-side pad electrode 611 consisting of the Ti layer havingthe thickness of about 100 nm, the Pd layer having the thickness ofabout 100 nm and the Au layer having the thickness of about 300 nm inascending order is formed on the upper surfaces of the insulator films610 to be in contact with the upper surface of the p-side ohmicelectrode 609, as show in FIG. 149. Further, the n-side electrode 612consisting of the Al layer having the thickness of about 6 nm, the Pdlayer having the thickness of about 10 nm and the Au layer having thethickness of about 300 nm from the side closer to the back surface ofthe n-type GaN substrate 601 is formed on the back surface of the n-typeGaN substrate 601. Thus, the nitride semiconductor laser elementaccording to the thirty-first embodiment is completed.

Thirty-Second Embodiment

Referring to FIGS. 165 to 167, an example of forming no ridge portiondissimilarly to the aforementioned thirty-first embodiment is describedwith reference to this thirty-second embodiment. The remaining structureof the thirty-second embodiment is similar to that of the aforementionedthirty-first embodiment.

According to this thirty-first embodiment, an n-type buffer layer 602,an n-type cladding layer 603 and an MQW emission layer 604 aresuccessively formed on an n-type GaN substrate 601, as shown in FIG.165. A p-type cladding layer 625 of p-type Al_(0.07)Ga_(0.03)N dopedwith Mg having a thickness of about 0.4 μm is formed on the MQW emissionlayer 604. A p-type contact layer 626 of p-type GaN doped with Mg havinga thickness of about 20 nm is formed on the p-type cladding layer 625.The p-type cladding layer 625 and the p-type contact layer 626 areexamples of the “second nitride semiconductor layer” in the presentinvention.

According to the thirty-second embodiment, ion-implanted lightabsorption layers 627 formed by ion-implanting carbon (C) are provided.These ion-implanted light absorption layers 607 have an implantationdepth (thickness) reaching the interior of the n-type cladding layer 603from the upper surface of the p-type contact layer 626. In other words,the ion-implanted light absorption layers 627 are formed up to positionsof a depth of about 0.3 μm from the surface of the n-type cladding layer603. The ion-implanted light absorption layers 627 are examples of the“light absorption layer” in the present invention. A region between sideends of the ion-implanted light absorption layers 627 functions as acurrent passing region 628. The width (width of optical confinement)between side ends of these ion-implanted light absorption layers 607varies with portions close to a cavity end surface of an element andportions close to the central portion. In other words, the width W31(about 1.5 μm) (see FIG. 166) between the side ends of portions of theion-implanted light absorption layers 627 located in the vicinity of thecavity end surface of the element has a size smaller than the width W32(about 7.5 μm) (see FIG. 167) between the side ends of the portions ofthe ion-implanted light absorption layers 627 located in the vicinity ofthe central portion of the element, as shown in FIGS. 166 and 167.Similarly to the aforementioned thirty-first embodiment shown in FIG.153, further, boundary regions between the portions of the ion-implantedlight absorption layers 627 located in the vicinity of the cavity endsurface of the element and the portions of the ion-implanted lightabsorption layers 627 located in the vicinity of the central portion ofthe element are formed in tapered shapes so that the width thereof isgradually changed.

As shown in FIG. 165, a p-side ohmic electrode 629 consisting of a Ptlayer having a thickness of about 1 nm and a Pd layer having a thicknessof about 20 nm in ascending order is formed on a region of the p-typecontact layer 626 formed with no ion-implanted light absorption layers627. Further, insulator films 630 of SiO₂ having a thickness of about100 nm to about 300 nm are formed on regions of the p-type contact layer626 formed with the ion-implanted light absorption layers 627. A p-sidepad electrode 631 consisting of a Ti layer having a thickness of about100 nm, a Pd layer having a thickness of about 100 nm and an Au layerhaving a thickness of about 300 nm in ascending order is formed on theupper surfaces of the p-side ohmic electrode 629 and the insulator films610. An n-side electrode 612 is formed on the back surface of the n-typeGaN substrate 601.

According to the thirty-second embodiment, as hereinabove described, theion-implanted light absorption layers 627 are provided while the portionbetween the side ends of these ion-implanted light absorption layers 627is made to function as the current passing region 628, wherebyfabrication steps can be simplified as compared with a case of forming aridge portion. On the other hand, element output characteristics arereduced as compared with a case of performing current narrowing with aridge portion. When employed for a playback information from an opticaldisk requiring no high output, however, no problem arises also when theoutput characteristics of the element are reduced.

The remaining effects of the thirty-second embodiment are similar tothose of the aforementioned thirty-first embodiment.

A fabrication process for a nitride semiconductor laser elementaccording to the thirty-second embodiment is now described withreference to FIGS. 165 and 168 to 172.

As shown in FIG. 168, layers up to the striped (elongated) p-side ohmicelectrode 629 and an SiO₂ film 613 are formed through a fabricationprocess similar to that of the thirty-first embodiment shown in FIGS.154 to 158. Thereafter an ion implantation mask 635 of positive resisthaving a thickness of about 1 μm is formed on prescribed regions of theupper surface and the side surfaces of the SiO₂ film 613, the sidesurfaces of the p-side ohmic electrode 629 and the upper surface of thep-type contact layer 626. At this time, the length L11 of the ionimplantation mask 615 from the cavity end surface of the element is setto about 20 μm, while the length L12 of a portion in the vicinity of thecentral portion of the element is set to about 500 μm. Further, theboundary region between the portion of the ion implantation mask 635located in the vicinity of the cavity end surface of the element and theportion of the ion implantation mask 635 located in the vicinity of thecentral portion of the element is formed in a tapered shape so that thewidth thereof is gradually changed, while the length L13 of the taperedportion is set to about 30 μm. In addition, the width of the portion ofthe ion implantation mask 635 close to the central portion of theelement is set to the width W32 (about 7.5 μm).

According to the thirty-second embodiment, the ion implantation mask 635is thereafter employed as a mask for ion-implanting carbon (C), as shownin FIG. 169. Thus, the ion-implanted light absorption layers 607 havingthe implantation depth (thickness) reaching the interior of the n-typecladding layer 603 from the upper surface of the p-type contact layer626 are formed. Ion implantation conditions for carbon are implantationenergy of about 95 keV, a dose of about 5×10¹³ cm⁻² and an implantationtemperature of the room temperature. This ion implantation is performedfrom a direction inclined by about 70 in the longitudinal direction ofthe p-side ohmic electrode 629. The width W31 between the side ends ofthe portions of the ion-implanted light absorption layers 627 located inthe vicinity of the cavity end surface of the element reaches the size(about 1.5 μm) substantially identical to the width of the p-side ohmicelectrode 629, while the width W32 between the side ends of the portionsof the ion-implanted light absorption layers 627 located in the vicinityof the central portion of the element reaches the size (about 7.5 μm)larger than the width of the p-side ohmic electrode 629. The regionbetween the side ends of the ion-implanted light absorption layers 627functions as the current passing region 628. Further, the boundaryregions between the portions of the ion-implanted light absorptionlayers 627 located in the vicinity of the cavity end surface of theelement and the portions of the ion-implanted light absorption layers627 located in the vicinity of the central portion of the element areformed in the tapered shapes so that the width thereof is graduallychanged.

Then, the ion implantation mask 635 is removed through a resiststripper. Thereafter the ion implantation mask 635 is completely removedby ashing with plasma. Thus, the state shown in FIG. 170 is obtained.

As shown in FIG. 171, the insulator film 630 of SiO₂ having thethickness of about 100 nm to about 300 nm is formed to cover the overallsurface.

Thereafter the SiO₂ film 613 and the portion of the insulator film 630located on the SiO₂ film 613 are removed, thereby exposing the p-sideohmic electrode 629 as shown in FIG. 172.

Finally, the p-side pad electrode 631 consisting of the Ti layer havingthe thickness of about 100 nm, the Pd layer having the thickness ofabout 100 nm and the Au layer having the thickness of about 300 nm inascending order is formed on the upper surfaces of the p-side ohmicelectrode 629 and the insulator films 630 to be in contact with theupper surface of the p-side ohmic electrode 609, as show in FIG. 165.Further, the n-side electrode 612 is formed on the back surface of then-type GaN substrate 601. Thus, the nitride semiconductor laser elementaccording to the thirty-second embodiment is completed.

The embodiments disclosed this time must be considered illustrative andnot restrictive in all points. The scope of the present invention isshown not by the above description of the embodiments but by the scopeof claim for patent, and all modifications within the meaning and rangeequivalent to the scope of claim for patent are included.

For example, while the ion-implanted light absorption layers have beenformed by ion-implanting any element of carbon, silicon, boron,phosphorus, magnesium or argon in each of the aforementionedembodiments, the present invention is not restricted to this but anotherelement may be ion-implanted. As to the implanted element, a dopanthaving conductivity reverse to the conductivity of the implanted-sidesemiconductor is preferably employed. Thus, the ion-implanted lightabsorption layers can be formed through ion implantation of a low dose.Further, a heavy element having a larger mass number than carbon ispreferably employed. Thus, channeling of implanted ions can beprevented. In addition, either a group 3 element such as Al, Ga or In ora group 5 element such as As or Sb may be implanted. In particular,phosphorus or As, forming a deep level (isoelectronic trap), can formsufficient light absorption layers at a low dose. Further, nitrogen,oxygen and neon etc. can be listed as elements other than the above.

While the ion-implanted light absorption layers having introducedelement concentration of about 1×10²⁰ cm⁻³ have been formed byion-implanting a large quantity of elements in each of theaforementioned embodiments, the present invention is not restricted tothis but the maximum value of the introduced element concentration maybe at least about 5×10¹⁹ cm⁻³. Further, the maximum value of the crystaldefect density of the ion-implanted light absorption layers may be atleast about 5.0×10¹⁸ cm⁻³. In addition, the maximum value of the lightabsorption coefficient of the ion-implanted light absorption layers maybe at least about 1×10⁴ cm⁻¹. If corresponding to any of theseconditions, transverse optical confinement can be sufficientlyperformed.

While the ion-implanted light absorption layers 57 have been formed bysimply ion-implanting carbon in the aforementioned sixth embodiment, thepresent invention is not restricted to this but heat treatment(annealing) may be performed after ion implantation. For example, heattreatment of about 10 minutes may be performed in an N₂/H₂ gas mixtureatmosphere of about 500° C. in the process of the sixth embodiment shownin FIG. 27. Cleanliness of the p-type contact layer 6 is maintained byperforming the heat treatment in the atmosphere containing H₂, wherebyexcellent p-side ohmic properties are obtained. In this case, the lightabsorption coefficient of the ion-implanted light absorption layers 57is so reduced that the threshold current is reduced. The atmosphere gasin the heat treatment may not be the N₂/H₂ gas mixture. For example, theatmosphere gas may be N₂/NH₃ gas or NH₃ gas. Thus, it is possible toreduce the number of crystal defects in the ion-implantation lightabsorption layers 57 while adjusting (reducing) the degree of lightabsorption (light absorption coefficient) through the heat treatment.

While ion implantation has been performed through the through filmhaving a first ion permeation region (SiO₂ of 10 nm) having firststopping power and a second ion permeation region (SiO₂ of 10 nm and Ptof 60 nm) having second stopping power more hardly permeating ions thanthe first ion permeation region in the aforementioned thirteenthembodiment, the present invention is not restricted to this but thefirst ion permeation region may be constituted of a through film havinga small thickness and the second ion permeation region may beconstituted of a through film having a large thickness. For example, thefirst ion permeation region may be constituted of an SiO₂ film of 10 nmand the second ion permeation region may be constituted of an SiO₂ filmof 300 nm, or the second ion permeation region may be constituted of aPt film of 60 nm while forming no through film on the first ionpermeation region. Further, the first ion permeation region may beconstituted of a through film consisting of a material having lowdensity and the second ion permeation region may be constituted of athrough film consisting of a material having high density. For example,the first ion permeation region may be constituted of an SiO₂ film of 60nm and the second ion permeation region may be constituted of a Pt filmof 60 nm.

While the case of electrically isolating p-type semiconductor layersfrom each other by forming the ion-implanted light absorption layers 187increased in resistance by ion implantation has been described withreference to the aforementioned eighteenth embodiment, the presentinvention is not restricted to this but may be applied to a case ofelectrically isolating a p-type semiconductor layer and an n-typesemiconductor layer from each other or a case of electrically isolatingn-type semiconductor layers from each other. Further, while the exampleof integrating a semiconductor laser by electric isolation resultingfrom ion implantation has been shown in the eighteenth embodiment, thepresent invention is not restricted to this but may be applied to a caseof performing integration of a light-emitting device such as alight-emitting diode, an electronic device such as an FET (Field EffectTransistor) or an HBT (Heterojunction Bipolar Transistor) or aphotodetector. Further, the present invention is also applicable to anIC (Integrated Circuit), an OEIC (Optoelectronic Integrated Circuit) oran optical IC.

While a striped optical confinement region has been formed and a nitridesemiconductor laser element having a waveguide structure of a stripedstructure has been formed in each of the aforementioned embodiments, acircular optical confinement region or the like may be formed by forminga circular non-implanted region or the like for preparing a verticalcavity type nitride semiconductor laser element.

While the ion-implanted light absorption layers 17 have been formed byion-implanting a large quantity of carbon in the aforementioned secondembodiment, the present invention is not restricted to this but ionimplantation may be performed with an element such as hydrogen or boronat a low dose. For example, boron may be implanted at implantationenergy of about 65 keV and a dose of about 1×10¹⁴ cm⁻². The peakintensity of the impurity concentration in this case is 8×10¹⁸ cm⁻³.

While the p-type contact layer of AlGaN or GaN has been employed in eachof the aforementioned embodiments, the present invention is notrestricted to this but a p-type contact layer consisting of InGaN may beemployed.

While the ion-implanted light absorption layers 307 have been formedonly on the surfaces of the flat portions of the p-type cladding layer305 other than the projecting portion constituting the ridge portion 308so that the side ends of the ion-implanted light absorption layers 307are arranged substantially immediately under the side ends of the ridgeportion 308 in the aforementioned twenty-first embodiment, the presentinvention is not restricted to this but the light absorption layers maybe formed to reach the regions formed with the MQW emission layer andthe n-type cladding layer so that the side ends of the light absorptionlayers are arranged substantially immediately under the side ends of theridge portion.

While the ion-implanted light absorption layers 327 (347) have beenformed to reach the n-type cladding layer 303 so that the side ends ofthe ion-implanted light absorption layers 327 (347) are arranged on thepositions separated from the side ends of the ridge portion 308 (348) ineach of the aforementioned twenty-second and twenty-third embodiments,the present invention is not restricted to this but the light absorptionlayers may be formed only on the surfaces of the flat portions of thep-type cladding layer other than the projecting portion constituting theridge portion so that the side ends of the light absorption layers arearranged on the positions separated from the side ends of the ridgeportion.

While the side ends of the ion-implanted light absorption layers 327(347) have been separated from the side ends of the ridge portion 308(348) in the range of not more than about 2 μm in each of theaforementioned twenty-second and twenty-third embodiments, the presentinvention is not restricted to this but the interval between the sideends of the light absorption layers and the side ends of the ridgeportion may be in the range of not more than 5 μm.

While no heat treatment has been performed after ion implantation ineach of the aforementioned twenty-first to twenty-fifth embodiments, thepresent invention is not restricted to this but heat treatment may beperformed after ion implantation, in order to adjust the absorptioncoefficient of the light absorption layers. In this case, the heattreatment is preferably performed in nitrogen gas having a flow rate ofabout 1 L/min. under a temperature condition of not more than about 400°C. Adjustment of the absorption coefficient is performed by controllingthe heat treatment time.

While the regions between the portions of the ion-implanted lightabsorption layers located in the vicinity of the cavity end surface ofthe element and the portions of the ion-implanted light absorptionlayers located in the vicinity of the central portion of the elementhave been formed in the tapered shapes in each of the aforementionedthirty-first and thirty-second embodiments, the present invention is notrestricted but a shape other than the tapered shape may be employed sofar as the width is gradually changed in the boundary regions betweenthe portions of the ion-implanted light absorption layers located in thevicinity of the cavity end surface of the element and the portions ofthe ion-implanted light absorption layers located in the vicinity of thecentral portion of the element. Further, the boundary regions betweenthe portions of the ion-implanted light absorption layers located in thevicinity of the cavity end surface of the element and the portions ofthe ion-implanted light absorption layers located in the vicinity of thecentral portion of the element may not be so shaped that the width isgradually changed. In this case, the structure of the element can besimplified. However, coupling loss is increased between the portionslocated in the vicinity of the cavity end surface of the element and theportions located in the vicinity of the central portion of the element,and hence the output characteristics are reduced.

1. A nitride semiconductor laser element comprising: a first nitridesemiconductor layer (2, 3, 172, 173, 302, 303, 602, 603); an emissionlayer (4, 174, 304, 604) formed on said first nitride semiconductorlayer; a second nitride semiconductor layer (5, 6, 175, 176, 305, 306,345, 365, 385, 605, 606, 625, 626) formed on said emission layer; and alight absorption layer (7, 17, 27, 37, 47, 57, 67, 77 b, 87 b, 97 b, 107b, 117 a, 127, 137, 147, 157 a, 157 b, 177 a, 187, 197 a, 207 a, 307,327, 347, 367, 387, 407, 437, 457, 477, 497, 607, 627) formed byintroducing a first impurity element into at least parts of regions ofsaid first nitride semiconductor layer and said second nitridesemiconductor layer other than a current passing region (8, 128, 138,148, 158 a, 158 b, 178, 188, 198, 208, 628) wherein said lightabsorption layer is formed excluding a first width, the nitridesemiconductor laser element further comprising an electrode layer cominginto ohmic contact with said second nitride semiconductor layer with awidth smaller than said first width.
 2. The nitride semiconductor laserelement according to claim 1, wherein the upper surface of said lightabsorption layer and the upper surface of said current passing regionare formed substantially on the same plane.
 3. The nitride semiconductorlaser element according to claim 1, wherein said second nitridesemiconductor layer has a projecting ridge portion (308, 348, 368, 388,608) including the current passing region.
 4. The nitride semiconductorlaser element according to claim 3, wherein the side ends of said lightabsorption layer (307, 407, 607) are substantially located immediatelyunder the side ends of said ridge portion.
 5. The nitride semiconductorlaser element according to claim 3, wherein the side ends of said lightabsorption layer (327, 347, 437, 457, 477, 497) are provided onpositions separated at prescribed intervals from the side ends of saidridge portion.
 6. The nitride semiconductor laser element according toclaim 3, wherein said light absorption layer (367, 387) is provided oneach side surface of said ridge portion.
 7. The nitride semiconductorlaser element according to claim 1, wherein said light absorption layerhas a larger number of crystal defects than said current passing region.8. The nitride semiconductor laser element according to claim 1, whereinsaid light absorption layer has a current blocking function.
 9. Thenitride semiconductor laser element according to claim 1, furthercomprising a current blocking layer (197 b, 207 b) formed by introducinga second impurity element into at least parts of the regions of saidfirst nitride semiconductor layer and said second nitride semiconductorlayer other than the current passing region.
 10. The nitridesemiconductor laser element according to claim 1, wherein said lightabsorption layer is formed by ion-implanting said first impurity elementinto the regions of said first nitride semiconductor layer and saidsecond nitride semiconductor layer other than the current passingregion.
 11. The nitride semiconductor laser element according to claim1, wherein said light absorption layer has either high resistance or areverse conductivity type to said current passing region.
 12. Thenitride semiconductor laser element according to claim 1, wherein saidfirst impurity element is an impurity element other than group 3 andgroup 5 elements.
 13. The nitride semiconductor laser element accordingto claim 1, wherein said first impurity element is an impurity elementhaving a larger mass number than carbon.
 14. The nitride semiconductorlaser element according to claim 1, wherein the maximum value of theimpurity concentration of said first impurity element is at least5.0×10¹⁹ cm⁻³.
 15. The nitride semiconductor laser element according toclaim 1, wherein the maximum value of crystal defect density of at leasteither said first nitride semiconductor layer or said second nitridesemiconductor layer containing said first impurity element is at least5×10¹⁸ cm⁻³.
 16. The nitride semiconductor laser element according toclaim 1, wherein the maximum value of the absorption coefficient of saidlight absorption layer is at least 1×10⁴ cm⁻¹.
 17. The nitridesemiconductor laser element according to claim 1, heat-treated afterintroduction of said first impurity element.
 18. The nitridesemiconductor laser element according to claim 1, wherein said lightabsorption layer is formed by ion implantation from a direction inclinedfrom the [0001] direction of a nitride semiconductor.
 19. The nitridesemiconductor laser element according to claim 9, wherein said currentblocking layer consists of a nitride semiconductor having highresistance.
 20. The nitride semiconductor laser element according toclaim 9, wherein said current passing region has a p type, and saidcurrent blocking layer contains hydrogen in higher density than saidcurrent passing region.
 21. The nitride semiconductor laser elementaccording to claim 9, wherein said current blocking layer has a reverseconductivity type to said current passing region.
 22. The nitridesemiconductor laser element according to claim 9, wherein said secondimpurity element is an impurity element other group 3 and group 5elements.
 23. The nitride semiconductor laser element according to claim9, wherein said current blocking layer is formed by ionimplanting saidsecond impurity element.
 24. The nitride semiconductor laser elementaccording to claim 9, wherein said current blocking layer is formed byion-implanting said second impurity element into the lower portion of amask layer obliquely from above.
 25. The nitride semiconductor laserelement according to claim 9, wherein said current blocking layer isformed by diffusing said second impurity element.
 26. The nitridesemiconductor laser element according to claim 9, wherein said lightabsorption layer is formed excluding a first width while said currentnarrowing layer is formed excluding a second width, said first width islarger than said second width, and a region of said second width isformed in a region of said first width.
 27. The nitride semiconductorlaser element according to claim 9, wherein said light absorption layeris formed separately from the emission layer by a first distance in thedepth direction while said current blocking layer is formed separatelyfrom said emission layer by a second distance in the depth direction,and said first distance is larger than said second distance.
 28. Thenitride semiconductor laser element according to claim 9, wherein theconcentration of said second impurity element in said current blockinglayer is lower than the concentration of said first impurity element insaid light absorption layer.
 29. The nitride semiconductor laser elementaccording to claim 9, wherein the density of crystal defects in saidcurrent blocking layer is lower than the density of crystal defects insaid light absorption layer.
 30. The nitride semiconductor laser elementaccording to claim 1, wherein the impurity concentration of said firstimpurity element in a portion of the emission layer corresponding to anupper or lower region of said light absorption layer is not more than5.0×10¹⁸ cm⁻³.
 31. The nitride semiconductor laser element according toclaim 1, wherein the density of crystal defects in a portion of saidemission layer located on an upper or lower region of said lightabsorption layer is not more than 5.0×10^(17 cm) ⁻³.
 32. The nitridesemiconductor laser element according to claim 1, wherein said firstnitride semiconductor layer and said second nitride semiconductor layerinclude a cladding layer, and the concentration of said first impurityelement is maximized in the cladding layer.
 33. The nitridesemiconductor laser element according to claim 1, wherein said lightabsorption layer is formed not to be formed in the emission layer. 34.The nitride semiconductor laser element according to claim 1, whereinsaid first nitride semiconductor layer and said second nitridesemiconductor layer include a cladding layer, and the density of crystaldefects in said light absorption layer is maximized in the claddinglayer.
 35. The nitride semiconductor laser element according to claim 1,wherein said first nitride semiconductor layer and said second nitridesemiconductor layer include a cladding layer, and the light absorptioncoefficient of said light absorption layer is maximized in the claddinglayer.
 36. The nitride semiconductor laser element according to claim 1,wherein said emission layer is formed on said first nitridesemiconductor layer after said first impurity element is introduced intosaid first nitride semiconductor layer.
 37. The nitride semiconductorlaser element according to claim 1, wherein the impurity concentrationof said first impurity element is maximized in the emission layer. 38.The nitride semiconductor laser element according to claim 1, whereinthe density of crystal defects in said light absorption layer ismaximized in the emission layer.
 39. The nitride semiconductor laserelement according to claim 1, wherein the light absorption coefficientof said light absorption layer is maximized in the emission layer. 40.The nitride semiconductor laser element according to claim 1, wherein acontact layer is formed on said second nitride semiconductor layer aftersaid light absorption layer is formed by introducing said first impurityelement into said second nitride semiconductor layer on said emissionlayer.
 41. The nitride semiconductor laser element according to claim 1,wherein said first impurity element is ion-implanted through a throughfilm.
 42. The nitride semiconductor laser element according to claim 41,wherein said through film is an insulator film.
 43. The nitridesemiconductor laser element according to claim 1, wherein said firstimpurity element is ion-implanted through a through film having a firstion permeation region having first stopping power and a second ionpermeation region having second stopping power more hardly permeatingions than said first ion permeation region.
 44. The nitridesemiconductor laser element according to claim 1, employing a first filmincluding a first region having first stopping power and a second regionhaving third stopping power hardly permeating ions as a through filmwhile employing said second region as a mask for ion-implanting saidfirst impurity element.
 45. The nitride semiconductor laser elementaccording to claim 1, further comprising an electrode layer formed onsaid second nitride semiconductor layer, wherein said first impurityelement is ion-implanted into said second nitride semiconductor layerthrough a through film with said electrode layer serving as a mask. 46.The nitride semiconductor laser element according to claim 1, wherein aninsulator film is formed on said light absorption layer.
 47. (canceled)48. The nitride semiconductor laser element according to claim 1,wherein said light absorption layer is formed excluding a first width,the nitride semiconductor laser element further comprising an electrodelayer coming into ohmic contact with said second nitride semiconductorlaser with a width larger than said first width.
 49. The nitridesemiconductor laser element according to claim 1, further comprising anelectric isolation region of high resistance formed by introducing athird impurity element into at least part of a region other than saidcurrent passing region over a region passing through the emission layerfrom the surface of said second nitride semiconductor layer.
 50. Thenitride semiconductor laser element according to claim 49, wherein saidelectric isolation region is formed by ion-implanting said thirdimpurity element.
 51. The nitride semiconductor laser element accordingto claim 49, introducing a fourth impurity element into the region otherthan said current passing region and at least part of a region otherthan said electric isolation region over the region passing through theemission layer from the surface of said second nitride semiconductorlayer so that the region passing through said emission layer from saidsecond nitride semiconductor layer has the same conductivity type assaid first nitride semiconductor layer.
 52. The nitride semiconductorlaser element according to claim 1, wherein said nitride semiconductorlaser element includes a nitride semiconductor laser element, assembledin a junction-down system, mounted on a base for heat radiation from thesurface of a side closer to said emission layer.
 53. The nitridesemiconductor laser element according to claim 1, wherein said lightabsorption layer (407, 437, 457, 477, 497) is divided into a pluralityof parts between said current passing region and side ends of theelement.
 54. The nitride semiconductor laser element according to claim53, wherein a portion of said light absorption layer (437 a, 497 a)closer to said current passing region has a smaller depth than a portionof said light absorption layer closer to the side ends of said element.55. The nitride semiconductor laser element according to claim 54,wherein the portion of the light absorption layer (437 a, 497 a) closerto said current passing region has a depth not reaching said emissionlayer.
 56. The nitride semiconductor laser element according to claim 1,wherein a first width (W21, W31) between side ends of said lightabsorption layer in the vicinity of a cavity end surface of the elementis smaller than a second width (W22, W33) between side ends of a portionof said light absorption layer in the vicinity of the central portion ofthe element.
 57. The nitride semiconductor laser element according toclaim 56, wherein a boundary region between a region of said lightabsorption layer (607, 627) having said first width and a region havingsaid second width has a width gradually enlarging to approach from saidfirst width to said second width.
 58. The nitride semiconductor laserelement according to claim 57, wherein the boundary region between theregion of said light absorption layer (607, 627) having said first widthand the region having said second width is formed in a tapered shape inplan view.
 59. A nitride semiconductor laser element comprising: a firstnitride semiconductor layer (2, 3, 172, 173, 302, 303, 602, 603); anemission layer (4, 174, 304, 604) formed on said first nitridesemiconductor layer; a second nitride semiconductor layer (5, 6, 175,176, 305, 306, 345, 365, 385, 605, 606, 625, 626) formed on saidemission layer; and a light absorption layer (7, 17, 27, 37, 47, 57, 67,77 b, 87 b, 97 b, 107 b, 117 a, 127, 137, 147, 157 a, 157 b, 177 a, 187,197 a, 207 a, 307, 327, 347, 367, 387, 407, 437, 457, 477, 497, 607,627) formed by introducing a first impurity element into at least partsof regions of said first nitride semiconductor layer and said secondnitride semiconductor layer other than a current passing region (8, 128,138, 148, 158 a, 158 b, 178, 188, 198, 208, 628), wherein said secondnitride semiconductor layer has a projecting ridge portion (308, 348,368, 388, 608) including a current passing region.
 60. A nitridesemiconductor laser element comprising: a first nitride semiconductorlayer (2, 3, 172, 173, 302, 303, 602, 603); an emission layer (4, 174,304, 604) formed on said first nitride semiconductor layer; a secondnitride semiconductor layer (5, 6, 175, 176, 305, 306, 345, 365, 385,605, 606, 625, 626) formed on said emission layer; and a lightabsorption layer (7, 17, 27, 37, 47, 57, 67, 77 b, 87 b, 97 b, 107 b,117 a, 127, 137, 147, 157 a, 157 b, 177 a, 187, 197 a, 207 a, 307, 327,347, 367, 387, 407, 437, 457, 477, 497, 607, 627) formed by introducinga first impurity element into at least parts of regions of said firstnitride semiconductor layer and said second nitride semiconductor layerother than a current passing region (8, 128, 138, 148, 158 a, 158 b,178, 188, 198, 208, 628), wherein an insulator film is provided on saidlight absorption layer.